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Date: Mon, 17 Jan 2011 22:59:13 +0900
From: Minchan Kim <minchan.kim@...il.com>
To: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Cc: Miklos Szeredi <miklos@...redi.hu>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
akpm@...ux-foundation.org, 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 Fri, Jan 14, 2011 at 10:00:37AM +0900, Daisuke Nishimura wrote:
> On Thu, 13 Jan 2011 14:35:09 +0100
> Miklos Szeredi <miklos@...redi.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@...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 +-
> > 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.
And it can conflict with https://patchwork.kernel.org/patch/470311/
I am not sure Andrew accept it easily although many mm guys already acked and reviewed it.
So I hope patch ordering is following as after mmotm release
1. https://lkml.org/lkml/2011/1/11/10 and https://lkml.org/lkml/2011/1/11/65
2. your patch
3. https://patchwork.kernel.org/patch/470311/
If you have a problem, please let me know it.
>
> Thanks,
> Daisuke Nishimura.
--
Kind regards,
Minchan Kim
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