On Thu, 16 Dec 2010, KAMEZAWA Hiroyuki wrote:
> On Wed, 15 Dec 2010 16:49:58 +0100
> Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
>
> > From: Miklos Szeredi <mszeredi@xxxxxxx>
> >
> > 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@xxxxxxx>
> > ---
> > 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);
>
> Hmm, then, the page will be recharged to "current" instead of the memcg
> where "old" was under control. Is this design ? If so, why ?
No, I just haven't thought about it.
Porbably charging "new" to where "old" was charged is the logical
thing to do here.
>
> In mm/migrate.c, following is called.
>
> charge = mem_cgroup_prepare_migration(page, newpage, &mem);
> ....do migration....
> if (!charge)
> mem_cgroup_end_migration(mem, page, newpage);
>
> BTW, off topic, in fuse/dev.c
>
> add_to_page_cache_locked(page)
This is the call which the above patch replaces with
replace_page_cache_page(). So if I fix replace_page_cache_page() to
charge "newpage" to the correct memory cgroup, that should solve all
problems, no?
Thanks for the review.
Miklos
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