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Message-Id: <E1PTCV4-0007sR-SO@pomaz-ex.szeredi.hu>
Date: Thu, 16 Dec 2010 12:59:58 +0100
From: Miklos Szeredi <miklos@...redi.hu>
To: Minchan Kim <minchan.kim@...il.com>
CC: miklos@...redi.hu, akpm@...ux-foundation.org,
linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: add replace_page_cache_page() function
On Thu, 16 Dec 2010, Minchan Kim wrote:
> On Thu, Dec 16, 2010 at 12:49 AM, Miklos Szeredi <miklos@...redi.hu> wrote:
> > From: Miklos Szeredi <mszeredi@...e.cz>
> >
> > 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.
>
> Please write down why fuse need this new atomic function in description.
Okay.
> >
> > Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>
> > ---
> > 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);
> >
>
> This function is exported.
> Please, add function description
Right, will do.
> > +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);
> > + if (error)
> > + goto out;
> > +
> > + error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
> > + if (error == 0) {
> > + 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_uncharge_cache_page(old);
> > + page_cache_release(old);
>
> Why do you release reference of old?
That's the page cache reference we release. Just like we acquire the
page cache reference for "new" above.
I suspect it's historic that page_cache_release() doesn't drop the
page cache ref.
Thanks for the review.
Miklos
> > + } else
> > + mem_cgroup_uncharge_cache_page(new);
> > +out:
> > + 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
> > Index: linux-2.6/include/linux/pagemap.h
> > ===================================================================
> > --- linux-2.6.orig/include/linux/pagemap.h 2010-12-15 16:39:39.000000000 +0100
> > +++ linux-2.6/include/linux/pagemap.h 2010-12-15 16:41:24.000000000 +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 2010-12-15 16:39:39.000000000 +0100
> > +++ linux-2.6/fs/fuse/dev.c 2010-12-15 16:41:24.000000000 +0100
> > @@ -729,14 +729,12 @@ 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))
> >
> > --
> > To unsubscribe, send a message with 'unsubscribe linux-mm' in
> > the body to majordomo@...ck.org. For more info on Linux MM,
> > see: http://www.linux-mm.org/ .
> > Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/
> > Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a>
> >
>
>
>
> --
> Kind regards,
> Minchan Kim
>
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