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Message-Id: <E1Pd1iF-0001jM-CV@pomaz-ex.szeredi.hu>
Date: Wed, 12 Jan 2011 15:30:11 +0100
From: Miklos Szeredi <miklos@...redi.hu>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC: minchan.kim@...il.com, miklos@...redi.hu,
akpm@...ux-foundation.org, nishimura@....nes.nec.co.jp,
linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] mm: add replace_page_cache_page() function
On Wed, 12 Jan 2011, KAMEZAWA Hiroyuki wrote:
> On Tue, 11 Jan 2011 23:25:28 +0900
> Minchan Kim <minchan.kim@...il.com> wrote:
>
> > On Tue, Jan 11, 2011 at 03:07:54PM +0100, Miklos Szeredi wrote:
> > > (resent with fixed CC list, sorry for the duplicate)
> > >
> > > Thanks for the review.
> > >
> > > Here's an updated patch. Modifications since the last post:
> > >
> > > - don't pass gfp_mask (since it's only able to deal with GFP_KERNEL
> > > anyway)
> > >
> >
> > I am not sure it's a good idea.
> > Now if we need just GFP_KERNEL, we can't make sure it in future.
> > Sometime we might need GFP_ATOMIC and friendd functions
> > (ex, add_to_page_cache_lru,add_to_page_cache_locked) already have gfp_mask.
> > It's a exported function so it's hard to modify it in future.
> >
> > I want to keep it.
> > Instead of removing it, we can change mem_cgroup_prepare_migration as
> > getting gfp_mask.
> >
> you're right.
Okay, makes sense.
Here's an updated patch.
Thanks,
Miklos
---
From: Miklos Szeredi <mszeredi@...e.cz>
Subject: mm: add replace_page_cache_page() function
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/memcontrol.h | 4 +-
include/linux/pagemap.h | 1
mm/filemap.c | 65 +++++++++++++++++++++++++++++++++++++++++++++
mm/memcontrol.c | 4 +-
5 files changed, 74 insertions(+), 10 deletions(-)
Index: linux-2.6/mm/filemap.c
===================================================================
--- linux-2.6.orig/mm/filemap.c 2011-01-12 14:50:18.000000000 +0100
+++ linux-2.6/mm/filemap.c 2011-01-12 14:51:25.000000000 +0100
@@ -387,6 +387,71 @@ int filemap_write_and_wait_range(struct
EXPORT_SYMBOL(filemap_write_and_wait_range);
/**
+ * replace_page_cache_page - replace a pagecache page with a new one
+ * @old: page to be replaced
+ * @new: page to replace with
+ * @gfp_mask: allocation mode
+ *
+ * This function replaces a page in the pagecache with a new one. On
+ * success it acquires the pagecache reference for the new page and
+ * drops it for the old page. Both the old and new pages must be
+ * locked. This function does not add the new page to the LRU, the
+ * caller must do that.
+ *
+ * The remove + add is atomic. The only way this function can fail is
+ * memory allocation failure.
+ */
+int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
+{
+ int error;
+ struct mem_cgroup *memcg = NULL;
+
+ VM_BUG_ON(!PageLocked(old));
+ VM_BUG_ON(!PageLocked(new));
+ VM_BUG_ON(new->mapping);
+
+ /*
+ * This is not page migration, but prepare_migration and
+ * end_migration does enough work for charge replacement.
+ *
+ * In the longer term we probably want a specialized function
+ * for moving the charge from old to new in a more efficient
+ * manner.
+ */
+ error = mem_cgroup_prepare_migration(old, new, &memcg, gfp_mask);
+ if (error)
+ return error;
+
+ error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
+ if (!error) {
+ 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();
+ page_cache_release(old);
+ mem_cgroup_end_migration(memcg, old, new, true);
+ } else {
+ mem_cgroup_end_migration(memcg, old, new, false);
+ }
+
+ 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
* @mapping: the page's address_space
Index: linux-2.6/include/linux/pagemap.h
===================================================================
--- linux-2.6.orig/include/linux/pagemap.h 2011-01-12 14:50:18.000000000 +0100
+++ linux-2.6/include/linux/pagemap.h 2011-01-12 14:50:31.000000000 +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 2011-01-12 14:50:18.000000000 +0100
+++ linux-2.6/fs/fuse/dev.c 2011-01-12 14:50:31.000000000 +0100
@@ -737,14 +737,12 @@ 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))
Index: linux-2.6/include/linux/memcontrol.h
===================================================================
--- linux-2.6.orig/include/linux/memcontrol.h 2011-01-12 14:50:19.000000000 +0100
+++ linux-2.6/include/linux/memcontrol.h 2011-01-12 14:53:13.000000000 +0100
@@ -91,7 +91,7 @@ extern struct cgroup_subsys_state *mem_c
extern int
mem_cgroup_prepare_migration(struct page *page,
- struct page *newpage, struct mem_cgroup **ptr);
+ struct page *newpage, struct mem_cgroup **ptr, gfp_t gfp_mask);
extern void mem_cgroup_end_migration(struct mem_cgroup *mem,
struct page *oldpage, struct page *newpage, bool migration_ok);
@@ -225,7 +225,7 @@ static inline struct cgroup_subsys_state
static inline int
mem_cgroup_prepare_migration(struct page *page, struct page *newpage,
- struct mem_cgroup **ptr)
+ struct mem_cgroup **ptr, gfp_t gfp_mask)
{
return 0;
}
Index: linux-2.6/mm/memcontrol.c
===================================================================
--- linux-2.6.orig/mm/memcontrol.c 2011-01-12 14:50:19.000000000 +0100
+++ linux-2.6/mm/memcontrol.c 2011-01-12 14:50:39.000000000 +0100
@@ -2767,7 +2767,7 @@ static inline int mem_cgroup_move_swap_a
* page belongs to.
*/
int mem_cgroup_prepare_migration(struct page *page,
- struct page *newpage, struct mem_cgroup **ptr)
+ struct page *newpage, struct mem_cgroup **ptr, gfp_t gfp_mask)
{
struct page_cgroup *pc;
struct mem_cgroup *mem = NULL;
@@ -2823,7 +2823,7 @@ int mem_cgroup_prepare_migration(struct
return 0;
*ptr = mem;
- ret = __mem_cgroup_try_charge(NULL, GFP_KERNEL, ptr, false);
+ ret = __mem_cgroup_try_charge(NULL, gfp_mask, ptr, false);
css_put(&mem->css);/* drop extra refcnt */
if (ret || *ptr == NULL) {
if (PageAnon(page)) {
--
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