fs/nfs/pagelist.c - kernel/mindspeed - Git at Google

 /*
  * linux/fs/nfs/pagelist.c
  *
  * A set of helper functions for managing NFS read and write requests.
  * The main purpose of these routines is to provide support for the
  * coalescing of several requests into a single RPC call.
  *
  * Copyright 2000, 2001 (c) Trond Myklebust <trond.myklebust@fys.uio.no>
  *
  */

 #include <linux/slab.h>
 #include <linux/file.h>
 #include <linux/sched.h>
 #include <linux/sunrpc/clnt.h>
 #include <linux/nfs3.h>
 #include <linux/nfs4.h>
 #include <linux/nfs_page.h>
 #include <linux/nfs_fs.h>
 #include <linux/nfs_mount.h>
 #include <linux/export.h>

 #include "internal.h"
 #include "pnfs.h"

 static struct kmem_cache *nfs_page_cachep;

 static inline struct nfs_page *
 nfs_page_alloc(void)
 {
 	struct nfs_page	*p = kmem_cache_zalloc(nfs_page_cachep, GFP_KERNEL);
 	if (p)
 		INIT_LIST_HEAD(&p->wb_list);
 	return p;
 }

 static inline void
 nfs_page_free(struct nfs_page *p)
 {
 	kmem_cache_free(nfs_page_cachep, p);
 }

 /**
  * nfs_create_request - Create an NFS read/write request.
  * @ctx: open context to use
  * @inode: inode to which the request is attached
  * @page: page to write
  * @offset: starting offset within the page for the write
  * @count: number of bytes to read/write
  *
  * The page must be locked by the caller. This makes sure we never
  * create two different requests for the same page.
  * User should ensure it is safe to sleep in this function.
  */
 struct nfs_page *
 nfs_create_request(struct nfs_open_context *ctx, struct inode *inode,
 		   struct page *page,
 		   unsigned int offset, unsigned int count)
 {
 	struct nfs_page		*req;

 	/* try to allocate the request struct */
 	req = nfs_page_alloc();
 	if (req == NULL)
 		return ERR_PTR(-ENOMEM);

 	/* get lock context early so we can deal with alloc failures */
 	req->wb_lock_context = nfs_get_lock_context(ctx);
 	if (req->wb_lock_context == NULL) {
 		nfs_page_free(req);
 		return ERR_PTR(-ENOMEM);
 	}

 	/* Initialize the request struct. Initially, we assume a
 	 * long write-back delay. This will be adjusted in
 	 * update_nfs_request below if the region is not locked. */
 	req->wb_page    = page;
 	atomic_set(&req->wb_complete, 0);
 	req->wb_index	= page->index;
 	page_cache_get(page);
 	BUG_ON(PagePrivate(page));
 	BUG_ON(!PageLocked(page));
 	BUG_ON(page->mapping->host != inode);
 	req->wb_offset  = offset;
 	req->wb_pgbase	= offset;
 	req->wb_bytes   = count;
 	req->wb_context = get_nfs_open_context(ctx);
 	kref_init(&req->wb_kref);
 	return req;
 }

 /**
  * nfs_unlock_request - Unlock request and wake up sleepers.
  * @req:
  */
 void nfs_unlock_request(struct nfs_page *req)
 {
 	if (!NFS_WBACK_BUSY(req)) {
 		printk(KERN_ERR "NFS: Invalid unlock attempted\n");
 		BUG();
 	}
 	smp_mb__before_clear_bit();
 	clear_bit(PG_BUSY, &req->wb_flags);
 	smp_mb__after_clear_bit();
 	wake_up_bit(&req->wb_flags, PG_BUSY);
 	nfs_release_request(req);
 }

 /**
  * nfs_set_page_tag_locked - Tag a request as locked
  * @req:
  */
 int nfs_set_page_tag_locked(struct nfs_page *req)
 {
 	if (!nfs_lock_request_dontget(req))
 		return 0;
 	if (test_bit(PG_MAPPED, &req->wb_flags))
 		radix_tree_tag_set(&NFS_I(req->wb_context->dentry->d_inode)->nfs_page_tree, req->wb_index, NFS_PAGE_TAG_LOCKED);
 	return 1;
 }

 /**
  * nfs_clear_page_tag_locked - Clear request tag and wake up sleepers
  */
 void nfs_clear_page_tag_locked(struct nfs_page *req)
 {
 	if (test_bit(PG_MAPPED, &req->wb_flags)) {
 		struct inode *inode = req->wb_context->dentry->d_inode;
 		struct nfs_inode *nfsi = NFS_I(inode);

 		spin_lock(&inode->i_lock);
 		radix_tree_tag_clear(&nfsi->nfs_page_tree, req->wb_index, NFS_PAGE_TAG_LOCKED);
 		nfs_unlock_request(req);
 		spin_unlock(&inode->i_lock);
 	} else
 		nfs_unlock_request(req);
 }

 /*
  * nfs_clear_request - Free up all resources allocated to the request
  * @req:
  *
  * Release page and open context resources associated with a read/write
  * request after it has completed.
  */
 static void nfs_clear_request(struct nfs_page *req)
 {
 	struct page *page = req->wb_page;
 	struct nfs_open_context *ctx = req->wb_context;
 	struct nfs_lock_context *l_ctx = req->wb_lock_context;

 	if (page != NULL) {
 		page_cache_release(page);
 		req->wb_page = NULL;
 	}
 	if (l_ctx != NULL) {
 		nfs_put_lock_context(l_ctx);
 		req->wb_lock_context = NULL;
 	}
 	if (ctx != NULL) {
 		put_nfs_open_context(ctx);
 		req->wb_context = NULL;
 	}
 }


 /**
  * nfs_release_request - Release the count on an NFS read/write request
  * @req: request to release
  *
  * Note: Should never be called with the spinlock held!
  */
 static void nfs_free_request(struct kref *kref)
 {
 	struct nfs_page *req = container_of(kref, struct nfs_page, wb_kref);

 	/* Release struct file and open context */
 	nfs_clear_request(req);
 	nfs_page_free(req);
 }

 void nfs_release_request(struct nfs_page *req)
 {
 	kref_put(&req->wb_kref, nfs_free_request);
 }

 static int nfs_wait_bit_uninterruptible(void *word)
 {
 	io_schedule();
 	return 0;
 }

 /**
  * nfs_wait_on_request - Wait for a request to complete.
  * @req: request to wait upon.
  *
  * Interruptible by fatal signals only.
  * The user is responsible for holding a count on the request.
  */
 int
 nfs_wait_on_request(struct nfs_page *req)
 {
 	return wait_on_bit(&req->wb_flags, PG_BUSY,
 			nfs_wait_bit_uninterruptible,
 			TASK_UNINTERRUPTIBLE);
 }

 bool nfs_generic_pg_test(struct nfs_pageio_descriptor *desc, struct nfs_page *prev, struct nfs_page *req)
 {
 	/*
 	 * FIXME: ideally we should be able to coalesce all requests
 	 * that are not block boundary aligned, but currently this
 	 * is problematic for the case of bsize < PAGE_CACHE_SIZE,
 	 * since nfs_flush_multi and nfs_pagein_multi assume you
 	 * can have only one struct nfs_page.
 	 */
 	if (desc->pg_bsize < PAGE_SIZE)
 		return 0;

 	return desc->pg_count + req->wb_bytes <= desc->pg_bsize;
 }
 EXPORT_SYMBOL_GPL(nfs_generic_pg_test);

 /**
  * nfs_pageio_init - initialise a page io descriptor
  * @desc: pointer to descriptor
  * @inode: pointer to inode
  * @doio: pointer to io function
  * @bsize: io block size
  * @io_flags: extra parameters for the io function
  */
 void nfs_pageio_init(struct nfs_pageio_descriptor *desc,
 		     struct inode *inode,
 		     const struct nfs_pageio_ops *pg_ops,
 		     size_t bsize,
 		     int io_flags)
 {
 	INIT_LIST_HEAD(&desc->pg_list);
 	desc->pg_bytes_written = 0;
 	desc->pg_count = 0;
 	desc->pg_bsize = bsize;
 	desc->pg_base = 0;
 	desc->pg_moreio = 0;
 	desc->pg_recoalesce = 0;
 	desc->pg_inode = inode;
 	desc->pg_ops = pg_ops;
 	desc->pg_ioflags = io_flags;
 	desc->pg_error = 0;
 	desc->pg_lseg = NULL;
 }

 /**
  * nfs_can_coalesce_requests - test two requests for compatibility
  * @prev: pointer to nfs_page
  * @req: pointer to nfs_page
  *
  * The nfs_page structures 'prev' and 'req' are compared to ensure that the
  * page data area they describe is contiguous, and that their RPC
  * credentials, NFSv4 open state, and lockowners are the same.
  *
  * Return 'true' if this is the case, else return 'false'.
  */
 static bool nfs_can_coalesce_requests(struct nfs_page *prev,
 				      struct nfs_page *req,
 				      struct nfs_pageio_descriptor *pgio)
 {
 	if (req->wb_context->cred != prev->wb_context->cred)
 		return false;
 	if (req->wb_lock_context->lockowner != prev->wb_lock_context->lockowner)
 		return false;
 	if (req->wb_context->state != prev->wb_context->state)
 		return false;
 	if (req->wb_index != (prev->wb_index + 1))
 		return false;
 	if (req->wb_pgbase != 0)
 		return false;
 	if (prev->wb_pgbase + prev->wb_bytes != PAGE_CACHE_SIZE)
 		return false;
 	return pgio->pg_ops->pg_test(pgio, prev, req);
 }

 /**
  * nfs_pageio_do_add_request - Attempt to coalesce a request into a page list.
  * @desc: destination io descriptor
  * @req: request
  *
  * Returns true if the request 'req' was successfully coalesced into the
  * existing list of pages 'desc'.
  */
 static int nfs_pageio_do_add_request(struct nfs_pageio_descriptor *desc,
 				     struct nfs_page *req)
 {
 	if (desc->pg_count != 0) {
 		struct nfs_page *prev;

 		prev = nfs_list_entry(desc->pg_list.prev);
 		if (!nfs_can_coalesce_requests(prev, req, desc))
 			return 0;
 	} else {
 		if (desc->pg_ops->pg_init)
 			desc->pg_ops->pg_init(desc, req);
 		desc->pg_base = req->wb_pgbase;
 	}
 	nfs_list_remove_request(req);
 	nfs_list_add_request(req, &desc->pg_list);
 	desc->pg_count += req->wb_bytes;
 	return 1;
 }

 /*
  * Helper for nfs_pageio_add_request and nfs_pageio_complete
  */
 static void nfs_pageio_doio(struct nfs_pageio_descriptor *desc)
 {
 	if (!list_empty(&desc->pg_list)) {
 		int error = desc->pg_ops->pg_doio(desc);
 		if (error < 0)
 			desc->pg_error = error;
 		else
 			desc->pg_bytes_written += desc->pg_count;
 	}
 	if (list_empty(&desc->pg_list)) {
 		desc->pg_count = 0;
 		desc->pg_base = 0;
 	}
 }

 /**
  * nfs_pageio_add_request - Attempt to coalesce a request into a page list.
  * @desc: destination io descriptor
  * @req: request
  *
  * Returns true if the request 'req' was successfully coalesced into the
  * existing list of pages 'desc'.
  */
 static int __nfs_pageio_add_request(struct nfs_pageio_descriptor *desc,
 			   struct nfs_page *req)
 {
 	while (!nfs_pageio_do_add_request(desc, req)) {
 		desc->pg_moreio = 1;
 		nfs_pageio_doio(desc);
 		if (desc->pg_error < 0)
 			return 0;
 		desc->pg_moreio = 0;
 		if (desc->pg_recoalesce)
 			return 0;
 	}
 	return 1;
 }

 static int nfs_do_recoalesce(struct nfs_pageio_descriptor *desc)
 {
 	LIST_HEAD(head);

 	do {
 		list_splice_init(&desc->pg_list, &head);
 		desc->pg_bytes_written -= desc->pg_count;
 		desc->pg_count = 0;
 		desc->pg_base = 0;
 		desc->pg_recoalesce = 0;

 		while (!list_empty(&head)) {
 			struct nfs_page *req;

 			req = list_first_entry(&head, struct nfs_page, wb_list);
 			nfs_list_remove_request(req);
 			if (__nfs_pageio_add_request(desc, req))
 				continue;
 			if (desc->pg_error < 0)
 				return 0;
 			break;
 		}
 	} while (desc->pg_recoalesce);
 	return 1;
 }

 int nfs_pageio_add_request(struct nfs_pageio_descriptor *desc,
 		struct nfs_page *req)
 {
 	int ret;

 	do {
 		ret = __nfs_pageio_add_request(desc, req);
 		if (ret)
 			break;
 		if (desc->pg_error < 0)
 			break;
 		ret = nfs_do_recoalesce(desc);
 	} while (ret);
 	return ret;
 }

 /**
  * nfs_pageio_complete - Complete I/O on an nfs_pageio_descriptor
  * @desc: pointer to io descriptor
  */
 void nfs_pageio_complete(struct nfs_pageio_descriptor *desc)
 {
 	for (;;) {
 		nfs_pageio_doio(desc);
 		if (!desc->pg_recoalesce)
 			break;
 		if (!nfs_do_recoalesce(desc))
 			break;
 	}
 }

 /**
  * nfs_pageio_cond_complete - Conditional I/O completion
  * @desc: pointer to io descriptor
  * @index: page index
  *
  * It is important to ensure that processes don't try to take locks
  * on non-contiguous ranges of pages as that might deadlock. This
  * function should be called before attempting to wait on a locked
  * nfs_page. It will complete the I/O if the page index 'index'
  * is not contiguous with the existing list of pages in 'desc'.
  */
 void nfs_pageio_cond_complete(struct nfs_pageio_descriptor *desc, pgoff_t index)
 {
 	if (!list_empty(&desc->pg_list)) {
 		struct nfs_page *prev = nfs_list_entry(desc->pg_list.prev);
 		if (index != prev->wb_index + 1)
 			nfs_pageio_complete(desc);
 	}
 }

 #define NFS_SCAN_MAXENTRIES 16
 /**
  * nfs_scan_list - Scan a list for matching requests
  * @nfsi: NFS inode
  * @dst: Destination list
  * @idx_start: lower bound of page->index to scan
  * @npages: idx_start + npages sets the upper bound to scan.
  * @tag: tag to scan for
  *
  * Moves elements from one of the inode request lists.
  * If the number of requests is set to 0, the entire address_space
  * starting at index idx_start, is scanned.
  * The requests are *not* checked to ensure that they form a contiguous set.
  * You must be holding the inode's i_lock when calling this function
  */
 int nfs_scan_list(struct nfs_inode *nfsi,
 		struct list_head *dst, pgoff_t idx_start,
 		unsigned int npages, int tag)
 {
 	struct nfs_page *pgvec[NFS_SCAN_MAXENTRIES];
 	struct nfs_page *req;
 	pgoff_t idx_end;
 	int found, i;
 	int res;
 	struct list_head *list;

 	res = 0;
 	if (npages == 0)
 		idx_end = ~0;
 	else
 		idx_end = idx_start + npages - 1;

 	for (;;) {
 		found = radix_tree_gang_lookup_tag(&nfsi->nfs_page_tree,
 				(void **)&pgvec[0], idx_start,
 				NFS_SCAN_MAXENTRIES, tag);
 		if (found <= 0)
 			break;
 		for (i = 0; i < found; i++) {
 			req = pgvec[i];
 			if (req->wb_index > idx_end)
 				goto out;
 			idx_start = req->wb_index + 1;
 			if (nfs_set_page_tag_locked(req)) {
 				kref_get(&req->wb_kref);
 				radix_tree_tag_clear(&nfsi->nfs_page_tree,
 						req->wb_index, tag);
 				list = pnfs_choose_commit_list(req, dst);
 				nfs_list_add_request(req, list);
 				res++;
 				if (res == INT_MAX)
 					goto out;
 			}
 		}
 		/* for latency reduction */
 		cond_resched_lock(&nfsi->vfs_inode.i_lock);
 	}
 out:
 	return res;
 }

 int __init nfs_init_nfspagecache(void)
 {
 	nfs_page_cachep = kmem_cache_create("nfs_page",
 					    sizeof(struct nfs_page),
 					    0, SLAB_HWCACHE_ALIGN,
 					    NULL);
 	if (nfs_page_cachep == NULL)
 		return -ENOMEM;

 	return 0;
 }

 void nfs_destroy_nfspagecache(void)
 {
 	kmem_cache_destroy(nfs_page_cachep);
 }
	/*
	* linux/fs/nfs/pagelist.c
	*
	* A set of helper functions for managing NFS read and write requests.
	* The main purpose of these routines is to provide support for the
	* coalescing of several requests into a single RPC call.
	*
	* Copyright 2000, 2001 (c) Trond Myklebust <trond.myklebust@fys.uio.no>
	*
	*/

	#include <linux/slab.h>
	#include <linux/file.h>
	#include <linux/sched.h>
	#include <linux/sunrpc/clnt.h>
	#include <linux/nfs3.h>
	#include <linux/nfs4.h>
	#include <linux/nfs_page.h>
	#include <linux/nfs_fs.h>
	#include <linux/nfs_mount.h>
	#include <linux/export.h>

	#include "internal.h"
	#include "pnfs.h"

	static struct kmem_cache *nfs_page_cachep;

	static inline struct nfs_page *
	nfs_page_alloc(void)
	{
	struct nfs_page *p = kmem_cache_zalloc(nfs_page_cachep, GFP_KERNEL);
	if (p)
	INIT_LIST_HEAD(&p->wb_list);
	return p;
	}

	static inline void
	nfs_page_free(struct nfs_page *p)
	{
	kmem_cache_free(nfs_page_cachep, p);
	}

	/**
	* nfs_create_request - Create an NFS read/write request.
	* @ctx: open context to use
	* @inode: inode to which the request is attached
	* @page: page to write
	* @offset: starting offset within the page for the write
	* @count: number of bytes to read/write
	*
	* The page must be locked by the caller. This makes sure we never
	* create two different requests for the same page.
	* User should ensure it is safe to sleep in this function.
	*/
	struct nfs_page *
	nfs_create_request(struct nfs_open_context ctx, struct inode inode,
	struct page *page,
	unsigned int offset, unsigned int count)
	{
	struct nfs_page *req;

	/* try to allocate the request struct */
	req = nfs_page_alloc();
	if (req == NULL)
	return ERR_PTR(-ENOMEM);

	/* get lock context early so we can deal with alloc failures */
	req->wb_lock_context = nfs_get_lock_context(ctx);
	if (req->wb_lock_context == NULL) {
	nfs_page_free(req);
	return ERR_PTR(-ENOMEM);
	}

	/* Initialize the request struct. Initially, we assume a
	* long write-back delay. This will be adjusted in
	* update_nfs_request below if the region is not locked. */
	req->wb_page = page;
	atomic_set(&req->wb_complete, 0);
	req->wb_index = page->index;
	page_cache_get(page);
	BUG_ON(PagePrivate(page));
	BUG_ON(!PageLocked(page));
	BUG_ON(page->mapping->host != inode);
	req->wb_offset = offset;
	req->wb_pgbase = offset;
	req->wb_bytes = count;
	req->wb_context = get_nfs_open_context(ctx);
	kref_init(&req->wb_kref);
	return req;
	}

	/**
	* nfs_unlock_request - Unlock request and wake up sleepers.
	* @req:
	*/
	void nfs_unlock_request(struct nfs_page *req)
	{
	if (!NFS_WBACK_BUSY(req)) {
	printk(KERN_ERR "NFS: Invalid unlock attempted\n");
	BUG();
	}
	smp_mb__before_clear_bit();
	clear_bit(PG_BUSY, &req->wb_flags);
	smp_mb__after_clear_bit();
	wake_up_bit(&req->wb_flags, PG_BUSY);
	nfs_release_request(req);
	}

	/**
	* nfs_set_page_tag_locked - Tag a request as locked
	* @req:
	*/
	int nfs_set_page_tag_locked(struct nfs_page *req)
	{
	if (!nfs_lock_request_dontget(req))
	return 0;
	if (test_bit(PG_MAPPED, &req->wb_flags))
	radix_tree_tag_set(&NFS_I(req->wb_context->dentry->d_inode)->nfs_page_tree, req->wb_index, NFS_PAGE_TAG_LOCKED);
	return 1;
	}

	/**
	* nfs_clear_page_tag_locked - Clear request tag and wake up sleepers
	*/
	void nfs_clear_page_tag_locked(struct nfs_page *req)
	{
	if (test_bit(PG_MAPPED, &req->wb_flags)) {
	struct inode *inode = req->wb_context->dentry->d_inode;
	struct nfs_inode *nfsi = NFS_I(inode);

	spin_lock(&inode->i_lock);
	radix_tree_tag_clear(&nfsi->nfs_page_tree, req->wb_index, NFS_PAGE_TAG_LOCKED);
	nfs_unlock_request(req);
	spin_unlock(&inode->i_lock);
	} else
	nfs_unlock_request(req);
	}

	/*
	* nfs_clear_request - Free up all resources allocated to the request
	* @req:
	*
	* Release page and open context resources associated with a read/write
	* request after it has completed.
	*/
	static void nfs_clear_request(struct nfs_page *req)
	{
	struct page *page = req->wb_page;
	struct nfs_open_context *ctx = req->wb_context;
	struct nfs_lock_context *l_ctx = req->wb_lock_context;

	if (page != NULL) {
	page_cache_release(page);
	req->wb_page = NULL;
	}
	if (l_ctx != NULL) {
	nfs_put_lock_context(l_ctx);
	req->wb_lock_context = NULL;
	}
	if (ctx != NULL) {
	put_nfs_open_context(ctx);
	req->wb_context = NULL;
	}
	}


	/**
	* nfs_release_request - Release the count on an NFS read/write request
	* @req: request to release
	*
	* Note: Should never be called with the spinlock held!
	*/
	static void nfs_free_request(struct kref *kref)
	{
	struct nfs_page *req = container_of(kref, struct nfs_page, wb_kref);

	/* Release struct file and open context */
	nfs_clear_request(req);
	nfs_page_free(req);
	}

	void nfs_release_request(struct nfs_page *req)
	{
	kref_put(&req->wb_kref, nfs_free_request);
	}

	static int nfs_wait_bit_uninterruptible(void *word)
	{
	io_schedule();
	return 0;
	}

	/**
	* nfs_wait_on_request - Wait for a request to complete.
	* @req: request to wait upon.
	*
	* Interruptible by fatal signals only.
	* The user is responsible for holding a count on the request.
	*/
	int
	nfs_wait_on_request(struct nfs_page *req)
	{
	return wait_on_bit(&req->wb_flags, PG_BUSY,
	nfs_wait_bit_uninterruptible,
	TASK_UNINTERRUPTIBLE);
	}

	bool nfs_generic_pg_test(struct nfs_pageio_descriptor desc, struct nfs_page prev, struct nfs_page *req)
	{
	/*
	* FIXME: ideally we should be able to coalesce all requests
	* that are not block boundary aligned, but currently this
	* is problematic for the case of bsize < PAGE_CACHE_SIZE,
	* since nfs_flush_multi and nfs_pagein_multi assume you
	* can have only one struct nfs_page.
	*/
	if (desc->pg_bsize < PAGE_SIZE)
	return 0;

	return desc->pg_count + req->wb_bytes <= desc->pg_bsize;
	}
	EXPORT_SYMBOL_GPL(nfs_generic_pg_test);

	/**
	* nfs_pageio_init - initialise a page io descriptor
	* @desc: pointer to descriptor
	* @inode: pointer to inode
	* @doio: pointer to io function
	* @bsize: io block size
	* @io_flags: extra parameters for the io function
	*/
	void nfs_pageio_init(struct nfs_pageio_descriptor *desc,
	struct inode *inode,
	const struct nfs_pageio_ops *pg_ops,
	size_t bsize,
	int io_flags)
	{
	INIT_LIST_HEAD(&desc->pg_list);
	desc->pg_bytes_written = 0;
	desc->pg_count = 0;
	desc->pg_bsize = bsize;
	desc->pg_base = 0;
	desc->pg_moreio = 0;
	desc->pg_recoalesce = 0;
	desc->pg_inode = inode;
	desc->pg_ops = pg_ops;
	desc->pg_ioflags = io_flags;
	desc->pg_error = 0;
	desc->pg_lseg = NULL;
	}

	/**
	* nfs_can_coalesce_requests - test two requests for compatibility
	* @prev: pointer to nfs_page
	* @req: pointer to nfs_page
	*
	* The nfs_page structures 'prev' and 'req' are compared to ensure that the
	* page data area they describe is contiguous, and that their RPC
	* credentials, NFSv4 open state, and lockowners are the same.
	*
	* Return 'true' if this is the case, else return 'false'.
	*/
	static bool nfs_can_coalesce_requests(struct nfs_page *prev,
	struct nfs_page *req,
	struct nfs_pageio_descriptor *pgio)
	{
	if (req->wb_context->cred != prev->wb_context->cred)
	return false;
	if (req->wb_lock_context->lockowner != prev->wb_lock_context->lockowner)
	return false;
	if (req->wb_context->state != prev->wb_context->state)
	return false;
	if (req->wb_index != (prev->wb_index + 1))
	return false;
	if (req->wb_pgbase != 0)
	return false;
	if (prev->wb_pgbase + prev->wb_bytes != PAGE_CACHE_SIZE)
	return false;
	return pgio->pg_ops->pg_test(pgio, prev, req);
	}

	/**
	* nfs_pageio_do_add_request - Attempt to coalesce a request into a page list.
	* @desc: destination io descriptor
	* @req: request
	*
	* Returns true if the request 'req' was successfully coalesced into the
	* existing list of pages 'desc'.
	*/
	static int nfs_pageio_do_add_request(struct nfs_pageio_descriptor *desc,
	struct nfs_page *req)
	{
	if (desc->pg_count != 0) {
	struct nfs_page *prev;

	prev = nfs_list_entry(desc->pg_list.prev);
	if (!nfs_can_coalesce_requests(prev, req, desc))
	return 0;
	} else {
	if (desc->pg_ops->pg_init)
	desc->pg_ops->pg_init(desc, req);
	desc->pg_base = req->wb_pgbase;
	}
	nfs_list_remove_request(req);
	nfs_list_add_request(req, &desc->pg_list);
	desc->pg_count += req->wb_bytes;
	return 1;
	}

	/*
	* Helper for nfs_pageio_add_request and nfs_pageio_complete
	*/
	static void nfs_pageio_doio(struct nfs_pageio_descriptor *desc)
	{
	if (!list_empty(&desc->pg_list)) {
	int error = desc->pg_ops->pg_doio(desc);
	if (error < 0)
	desc->pg_error = error;
	else
	desc->pg_bytes_written += desc->pg_count;
	}
	if (list_empty(&desc->pg_list)) {
	desc->pg_count = 0;
	desc->pg_base = 0;
	}
	}

	/**
	* nfs_pageio_add_request - Attempt to coalesce a request into a page list.
	* @desc: destination io descriptor
	* @req: request
	*
	* Returns true if the request 'req' was successfully coalesced into the
	* existing list of pages 'desc'.
	*/
	static int __nfs_pageio_add_request(struct nfs_pageio_descriptor *desc,
	struct nfs_page *req)
	{
	while (!nfs_pageio_do_add_request(desc, req)) {
	desc->pg_moreio = 1;
	nfs_pageio_doio(desc);
	if (desc->pg_error < 0)
	return 0;
	desc->pg_moreio = 0;
	if (desc->pg_recoalesce)
	return 0;
	}
	return 1;
	}

	static int nfs_do_recoalesce(struct nfs_pageio_descriptor *desc)
	{
	LIST_HEAD(head);

	do {
	list_splice_init(&desc->pg_list, &head);
	desc->pg_bytes_written -= desc->pg_count;
	desc->pg_count = 0;
	desc->pg_base = 0;
	desc->pg_recoalesce = 0;

	while (!list_empty(&head)) {
	struct nfs_page *req;

	req = list_first_entry(&head, struct nfs_page, wb_list);
	nfs_list_remove_request(req);
	if (__nfs_pageio_add_request(desc, req))
	continue;
	if (desc->pg_error < 0)
	return 0;
	break;
	}
	} while (desc->pg_recoalesce);
	return 1;
	}

	int nfs_pageio_add_request(struct nfs_pageio_descriptor *desc,
	struct nfs_page *req)
	{
	int ret;

	do {
	ret = __nfs_pageio_add_request(desc, req);
	if (ret)
	break;
	if (desc->pg_error < 0)
	break;
	ret = nfs_do_recoalesce(desc);
	} while (ret);
	return ret;
	}

	/**
	* nfs_pageio_complete - Complete I/O on an nfs_pageio_descriptor
	* @desc: pointer to io descriptor
	*/
	void nfs_pageio_complete(struct nfs_pageio_descriptor *desc)
	{
	for (;;) {
	nfs_pageio_doio(desc);
	if (!desc->pg_recoalesce)
	break;
	if (!nfs_do_recoalesce(desc))
	break;
	}
	}

	/**
	* nfs_pageio_cond_complete - Conditional I/O completion
	* @desc: pointer to io descriptor
	* @index: page index
	*
	* It is important to ensure that processes don't try to take locks
	* on non-contiguous ranges of pages as that might deadlock. This
	* function should be called before attempting to wait on a locked
	* nfs_page. It will complete the I/O if the page index 'index'
	* is not contiguous with the existing list of pages in 'desc'.
	*/
	void nfs_pageio_cond_complete(struct nfs_pageio_descriptor *desc, pgoff_t index)
	{
	if (!list_empty(&desc->pg_list)) {
	struct nfs_page *prev = nfs_list_entry(desc->pg_list.prev);
	if (index != prev->wb_index + 1)
	nfs_pageio_complete(desc);
	}
	}

	#define NFS_SCAN_MAXENTRIES 16
	/**
	* nfs_scan_list - Scan a list for matching requests
	* @nfsi: NFS inode
	* @dst: Destination list
	* @idx_start: lower bound of page->index to scan
	* @npages: idx_start + npages sets the upper bound to scan.
	* @tag: tag to scan for
	*
	* Moves elements from one of the inode request lists.
	* If the number of requests is set to 0, the entire address_space
	* starting at index idx_start, is scanned.
	* The requests are not checked to ensure that they form a contiguous set.
	* You must be holding the inode's i_lock when calling this function
	*/
	int nfs_scan_list(struct nfs_inode *nfsi,
	struct list_head *dst, pgoff_t idx_start,
	unsigned int npages, int tag)
	{
	struct nfs_page *pgvec[NFS_SCAN_MAXENTRIES];
	struct nfs_page *req;
	pgoff_t idx_end;
	int found, i;
	int res;
	struct list_head *list;

	res = 0;
	if (npages == 0)
	idx_end = ~0;
	else
	idx_end = idx_start + npages - 1;

	for (;;) {
	found = radix_tree_gang_lookup_tag(&nfsi->nfs_page_tree,
	(void **)&pgvec[0], idx_start,
	NFS_SCAN_MAXENTRIES, tag);
	if (found <= 0)
	break;
	for (i = 0; i < found; i++) {
	req = pgvec[i];
	if (req->wb_index > idx_end)
	goto out;
	idx_start = req->wb_index + 1;
	if (nfs_set_page_tag_locked(req)) {
	kref_get(&req->wb_kref);
	radix_tree_tag_clear(&nfsi->nfs_page_tree,
	req->wb_index, tag);
	list = pnfs_choose_commit_list(req, dst);
	nfs_list_add_request(req, list);
	res++;
	if (res == INT_MAX)
	goto out;
	}
	}
	/* for latency reduction */
	cond_resched_lock(&nfsi->vfs_inode.i_lock);
	}
	out:
	return res;
	}

	int __init nfs_init_nfspagecache(void)
	{
	nfs_page_cachep = kmem_cache_create("nfs_page",
	sizeof(struct nfs_page),
	0, SLAB_HWCACHE_ALIGN,
	NULL);
	if (nfs_page_cachep == NULL)
	return -ENOMEM;

	return 0;
	}

	void nfs_destroy_nfspagecache(void)
	{
	kmem_cache_destroy(nfs_page_cachep);
	}