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Date: Tue, 11 Jan 2011 11:29:49 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: Miklos Szeredi <miklos@...redi.hu>
Cc: akpm@...ux-foundation.org, minchan.kim@...il.com,
linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>
Subject: Re: [PATCH] mm: add replace_page_cache_page() function
On Fri, 07 Jan 2011 19:22:41 +0100
Miklos Szeredi <miklos@...redi.hu> wrote:
> Here's an updated patch, addressing the review comments.
>
> Hiroyuki-san, can you please review the newly introduced
> mem_cgroup_replace_cache_page(), as I'm not fully familiar with the
> memory cgroup code.
>
Ok. Ccing Nishimura. see below.
> 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 | 8 +++++++
> include/linux/pagemap.h | 1
> mm/filemap.c | 50 +++++++++++++++++++++++++++++++++++++++++++++
> mm/memcontrol.c | 38 ++++++++++++++++++++++++++++++++++
> 5 files changed, 101 insertions(+), 6 deletions(-)
>
> Index: linux-2.6/mm/filemap.c
> ===================================================================
> --- linux-2.6.orig/mm/filemap.c 2011-01-07 17:53:39.000000000 +0100
> +++ linux-2.6/mm/filemap.c 2011-01-07 19:14:45.000000000 +0100
> @@ -390,6 +390,56 @@ 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: page 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
> + * drop 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;
> +
> + VM_BUG_ON(!PageLocked(old));
> + VM_BUG_ON(!PageLocked(new));
> + VM_BUG_ON(new->mapping);
> +
> + 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();
> + mem_cgroup_replace_cache_page(old, new);
> + page_cache_release(old);
> + }
> +
> + 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 2011-01-07 17:53:39.000000000 +0100
> +++ linux-2.6/include/linux/pagemap.h 2011-01-07 19:14:45.000000000 +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 2011-01-07 17:53:39.000000000 +0100
> +++ linux-2.6/fs/fuse/dev.c 2011-01-07 19:14:45.000000000 +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 2011-01-07 17:53:39.000000000 +0100
> +++ linux-2.6/include/linux/memcontrol.h 2011-01-07 19:14:45.000000000 +0100
> @@ -95,6 +95,9 @@ mem_cgroup_prepare_migration(struct page
> extern void mem_cgroup_end_migration(struct mem_cgroup *mem,
> struct page *oldpage, struct page *newpage);
>
> +extern void mem_cgroup_replace_cache_page(struct page *oldpage,
> + struct page *newpage);
> +
> /*
> * For memory reclaim.
> */
> @@ -236,6 +239,11 @@ static inline void mem_cgroup_end_migrat
> {
> }
>
> +static inline void mem_cgroup_replace_cache_page(struct page *oldpage,
> + struct page *newpage)
> +{
> +}
> +
> static inline int mem_cgroup_get_reclaim_priority(struct mem_cgroup *mem)
> {
> return 0;
> Index: linux-2.6/mm/memcontrol.c
> ===================================================================
> --- linux-2.6.orig/mm/memcontrol.c 2011-01-07 17:53:39.000000000 +0100
> +++ linux-2.6/mm/memcontrol.c 2011-01-07 19:20:41.000000000 +0100
> @@ -2905,6 +2905,44 @@ void mem_cgroup_end_migration(struct mem
> }
>
> /*
> + * This function moves the charge from oldpage to newpage. The new
> + * page must not be already charged.
> + */
> +void mem_cgroup_replace_cache_page(struct page *oldpage, struct page *newpage)
> +{
> + struct page_cgroup *old_pc;
> + struct page_cgroup *new_pc;
> + struct mem_cgroup *mem;
> +
> + if (mem_cgroup_disabled())
> + return;
> +
> + old_pc = lookup_page_cgroup(oldpage);
> + lock_page_cgroup(old_pc);
> + if (!PageCgroupUsed(old_pc)) {
> + unlock_page_cgroup(old_pc);
> + return;
> + }
> +
> + mem = old_pc->mem_cgroup;
> + css_get(&mem->css);
> + ClearPageCgroupUsed(old_pc);
> + unlock_page_cgroup(old_pc);
> +
> + new_pc = lookup_page_cgroup(newpage);
> + lock_page_cgroup(new_pc);
> + BUG_ON(PageCgroupUsed(new_pc));
> +
> + new_pc->mem_cgroup = mem;
> + smp_wmb();
> + SetPageCgroupCache(new_pc);
> + SetPageCgroupUsed(new_pc);
> + unlock_page_cgroup(new_pc);
> + css_put(&mem->css);
> +}
I think some of moving flags are lacked and this new function is not necessary.
What I recommend is below. (Please see the newest -mm because of a bug fix for
mem cgroup) Considering page management on radix-tree, it can be considerd as
a kind of page-migration, which replaces pages on radix-tree.
==
> +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);
> +
struct mem_cgroup *memcg;
error = mem_cgroup_prepare_migration(old, new, &memcg);
#
# This function will charge against "newpage". But this expects
# the caller allows GFP_KERNEL gfp_mask.
# After this, the newpage is in "charged" state.
if (error)
return -ENOMEM;
> + 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();
> + mem_cgroup_replace_cache_page(old, new); <== remove this.
mem_cgroup_end_migraton(memcg, old, new, true);
> + page_cache_release(old);
> + }
else
mem_cgroup_end_migration(memcg, old, new, false);
# Here, if the 4th argument is true, old page is uncharged.
# if the 4th argument is false, the new page is uncharged.
# Then, "charge" of the old page will be migrated onto the new page
# if replacement is done.
> +
> + return error;
> +}
> +EXPORT_SYMBOL_GPL(replace_page_cache_page);
> +
==
I think this is enough simple and this covers all memory cgroup's racy
problems.
Thanks,
-Kame
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