path: root/fs/fscache/page.c

/* Cache page management and data I/O routines
 *
 * Copyright (C) 2004-2008 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#define FSCACHE_DEBUG_LEVEL PAGE
#include <linux/module.h>
#include <linux/fscache-cache.h>
#include <linux/buffer_head.h>
#include <linux/pagevec.h>
#include <linux/slab.h>
#include "internal.h"

/*
 * check to see if a page is being written to the cache
 */
bool __fscache_check_page_write(struct fscache_cookie *cookie, struct page *page)
{
	void *val;

	rcu_read_lock();
	val = radix_tree_lookup(&cookie->stores, page->index);
	rcu_read_unlock();

	return val != NULL;
}
EXPORT_SYMBOL(__fscache_check_page_write);

/*
 * wait for a page to finish being written to the cache
 */
void __fscache_wait_on_page_write(struct fscache_cookie *cookie, struct page *page)
{
	wait_queue_head_t *wq = bit_waitqueue(&cookie->flags, 0);

	wait_event(*wq, !__fscache_check_page_write(cookie, page));
}
EXPORT_SYMBOL(__fscache_wait_on_page_write);

/*
 * decide whether a page can be released, possibly by cancelling a store to it
 * - we're allowed to sleep if __GFP_WAIT is flagged
 */
bool __fscache_maybe_release_page(struct fscache_cookie *cookie,
				  struct page *page,
				  gfp_t gfp)
{
	struct page *xpage;
	void *val;

	_enter("%p,%p,%x", cookie, page, gfp);

try_again:
	rcu_read_lock();
	val = radix_tree_lookup(&cookie->stores, page->index);
	if (!val) {
		rcu_read_unlock();
		fscache_stat(&fscache_n_store_vmscan_not_storing);
		__fscache_uncache_page(cookie, page);
		return true;
	}

	/* see if the page is actually undergoing storage - if so we can't get
	 * rid of it till the cache has finished with it */
	if (radix_tree_tag_get(&cookie->stores, page->index,
			       FSCACHE_COOKIE_STORING_TAG)) {
		rcu_read_unlock();
		goto page_busy;
	}

	/* the page is pending storage, so we attempt to cancel the store and
	 * discard the store request so that the page can be reclaimed */
	spin_lock(&cookie->stores_lock);
	rcu_read_unlock();

	if (radix_tree_tag_get(&cookie->stores, page->index,
			       FSCACHE_COOKIE_STORING_TAG)) {
		/* the page started to undergo storage whilst we were looking,
		 * so now we can only wait or return */
		spin_unlock(&cookie->stores_lock);
		goto page_busy;
	}

	xpage = radix_tree_delete(&cookie->stores, page->index);
	spin_unlock(&cookie->stores_lock);

	if (xpage) {
		fscache_stat(&fscache_n_store_vmscan_cancelled);
		fscache_stat(&fscache_n_store_radix_deletes);
		ASSERTCMP(xpage, ==, page);
	} else {
		fscache_stat(&fscache_n_store_vmscan_gone);
	}

	wake_up_bit(&cookie->flags, 0);
	if (xpage)
		page_cache_release(xpage);
	__fscache_uncache_page(cookie, page);
	return true;

page_busy:
	/* We will wait here if we're allowed to, but that could deadlock the
	 * allocator as the work threads writing to the cache may all end up
	 * sleeping on memory allocation, so we may need to impose a timeout
	 * too. */
	if (!(gfp & __GFP_WAIT) || !(gfp & __GFP_FS)) {
		fscache_stat(&fscache_n_store_vmscan_busy);
		return false;
	}

	fscache_stat(&fscache_n_store_vmscan_wait);
	__fscache_wait_on_page_write(cookie, page);
	gfp &= ~__GFP_WAIT;
	goto try_again;
}
EXPORT_SYMBOL(__fscache_maybe_release_page);

/*
 * note that a page has finished being written to the cache
 */
static void fscache_end_page_write(struct fscache_object