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SubjectRe: [PATCH v3] mm: add replace_page_cache_page() function
On Thu, 13 Jan 2011 14:35:09 +0100
Miklos Szeredi <miklos@szeredi.hu> wrote:

> > Seems nicer. But you didn't fixed the caller of prepare_migraton()
> > in mm/migrate.c (I think this is the only caller..)
> >
> > please modify it, too.
>
> Right you are. Thanks for the review.
>
> Updated patch attached.
>
> Thanks,
> Miklos
> ---
>
>
> From: Miklos Szeredi <mszeredi@suse.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@suse.cz>
> ---
> fs/fuse/dev.c | 10 ++----
> include/linux/memcontrol.h | 4 +-
> include/linux/pagemap.h | 1
> mm/filemap.c | 65 +++++++++++++++++++++++++++++++++++++++++++++
> mm/memcontrol.c | 4 +-
> mm/migrate.c | 2 -
> 6 files changed, 75 insertions(+), 11 deletions(-)
>
> Index: linux-2.6/mm/filemap.c
> ===================================================================
> --- linux-2.6.orig/mm/filemap.c 2011-01-12 15:28:56.000000000 +0100
> +++ linux-2.6/mm/filemap.c 2011-01-13 13:37:41.000000000 +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 15:28:56.000000000 +0100
> +++ linux-2.6/include/linux/pagemap.h 2011-01-13 13:37:41.000000000 +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 15:28:56.000000000 +0100
> +++ linux-2.6/fs/fuse/dev.c 2011-01-13 13:37:41.000000000 +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 2011-01-13 13:37:40.000000000 +0100
> +++ linux-2.6/include/linux/memcontrol.h 2011-01-13 13:37:41.000000000 +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 2011-01-13 13:37:40.000000000 +0100
> +++ linux-2.6/mm/memcontrol.c 2011-01-13 13:37:41.000000000 +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)) {
> Index: linux-2.6/mm/migrate.c
> ===================================================================
> --- linux-2.6.orig/mm/migrate.c 2011-01-13 13:37:40.000000000 +0100
> +++ linux-2.6/mm/migrate.c 2011-01-13 13:38:55.000000000 +0100
> @@ -657,7 +657,7 @@ static int unmap_and_move(new_page_t get
> }
>
> /* charge against new page */
> - charge = mem_cgroup_prepare_migration(page, newpage, &mem);
> + charge = mem_cgroup_prepare_migration(page, newpage, &mem, GFP_KERNEL);
> if (charge == -ENOMEM) {
> rc = -ENOMEM;
> goto unlock;
This patch looks good and I want to ack, but this patch can conflict with patches
in https://lkml.org/lkml/2011/1/11/10 and https://lkml.org/lkml/2011/1/11/65.
So I think you'd better coordinate with Minchan.

Thanks,
Daisuke Nishimura.


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