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Message-Id: <E1PStc6-0006Cd-0Z@pomaz-ex.szeredi.hu>
Date: Wed, 15 Dec 2010 16:49:58 +0100
From: Miklos Szeredi <miklos@...redi.hu>
To: akpm@...ux-foundation.org
CC: linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: [PATCH] mm: add replace_page_cache_page() function
From: Miklos Szeredi <mszeredi@...e.cz>
This function basically does:
remove_from_page_cache(old);
page_cache_release(old);
add_to_page_cache_locked(new);
Except it does this atomically, so there's no possibility for the
"add" to fail because of a race.
This is used by fuse to move pages into the page cache.
Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>
---
fs/fuse/dev.c | 10 ++++------
include/linux/pagemap.h | 1 +
mm/filemap.c | 41 +++++++++++++++++++++++++++++++++++++++++
3 files changed, 46 insertions(+), 6 deletions(-)
Index: linux-2.6/mm/filemap.c
===================================================================
--- linux-2.6.orig/mm/filemap.c 2010-12-15 16:39:55.000000000 +0100
+++ linux-2.6/mm/filemap.c 2010-12-15 16:41:24.000000000 +0100
@@ -389,6 +389,47 @@ int filemap_write_and_wait_range(struct
}
EXPORT_SYMBOL(filemap_write_and_wait_range);
+int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
+{
+ int error;
+
+ VM_BUG_ON(!PageLocked(old));
+ VM_BUG_ON(!PageLocked(new));
+ VM_BUG_ON(new->mapping);
+
+ error = mem_cgroup_cache_charge(new, current->mm,
+ gfp_mask & GFP_RECLAIM_MASK);
+ if (error)
+ goto out;
+
+ error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
+ if (error == 0) {
+ struct address_space *mapping = old->mapping;
+ pgoff_t offset = old->index;
+
+ page_cache_get(new);
+ new->mapping = mapping;
+ new->index = offset;
+
+ spin_lock_irq(&mapping->tree_lock);
+ __remove_from_page_cache(old);
+ error = radix_tree_insert(&mapping->page_tree, offset, new);
+ BUG_ON(error);
+ mapping->nrpages++;
+ __inc_zone_page_state(new, NR_FILE_PAGES);
+ if (PageSwapBacked(new))
+ __inc_zone_page_state(new, NR_SHMEM);
+ spin_unlock_irq(&mapping->tree_lock);
+ radix_tree_preload_end();
+ mem_cgroup_uncharge_cache_page(old);
+ page_cache_release(old);
+ } else
+ mem_cgroup_uncharge_cache_page(new);
+out:
+ return error;
+}
+EXPORT_SYMBOL_GPL(replace_page_cache_page);
+
/**
* add_to_page_cache_locked - add a locked page to the pagecache
* @page: page to add
Index: linux-2.6/include/linux/pagemap.h
===================================================================
--- linux-2.6.orig/include/linux/pagemap.h 2010-12-15 16:39:39.000000000 +0100
+++ linux-2.6/include/linux/pagemap.h 2010-12-15 16:41:24.000000000 +0100
@@ -457,6 +457,7 @@ int add_to_page_cache_lru(struct page *p
pgoff_t index, gfp_t gfp_mask);
extern void remove_from_page_cache(struct page *page);
extern void __remove_from_page_cache(struct page *page);
+int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask);
/*
* Like add_to_page_cache_locked, but used to add newly allocated pages:
Index: linux-2.6/fs/fuse/dev.c
===================================================================
--- linux-2.6.orig/fs/fuse/dev.c 2010-12-15 16:39:39.000000000 +0100
+++ linux-2.6/fs/fuse/dev.c 2010-12-15 16:41:24.000000000 +0100
@@ -729,14 +729,12 @@ static int fuse_try_move_page(struct fus
if (WARN_ON(PageMlocked(oldpage)))
goto out_fallback_unlock;
- remove_from_page_cache(oldpage);
- page_cache_release(oldpage);
-
- err = add_to_page_cache_locked(newpage, mapping, index, GFP_KERNEL);
+ err = replace_page_cache_page(oldpage, newpage, GFP_KERNEL);
if (err) {
- printk(KERN_WARNING "fuse_try_move_page: failed to add page");
- goto out_fallback_unlock;
+ unlock_page(newpage);
+ return err;
}
+
page_cache_get(newpage);
if (!(buf->flags & PIPE_BUF_FLAG_LRU))
--
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