Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752724Ab0LPMAT (ORCPT ); Thu, 16 Dec 2010 07:00:19 -0500 Received: from fxip-0047f.externet.hu ([88.209.222.127]:44432 "EHLO pomaz-ex.szeredi.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751995Ab0LPMAN (ORCPT ); Thu, 16 Dec 2010 07:00:13 -0500 To: Minchan Kim CC: miklos@szeredi.hu, akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org In-reply-to: (message from Minchan Kim on Thu, 16 Dec 2010 08:22:55 +0900) Subject: Re: [PATCH] mm: add replace_page_cache_page() function References: MIME-version: 1.0 Content-type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Message-Id: From: Miklos Szeredi Date: Thu, 16 Dec 2010 12:59:58 +0100 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5964 Lines: 153 On Thu, 16 Dec 2010, Minchan Kim wrote: > On Thu, Dec 16, 2010 at 12:49 AM, Miklos Szeredi wrote: > > From: Miklos Szeredi > > > > 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 > > --- > >  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@kvack.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: email@kvack.org > > > > > > -- > Kind regards, > Minchan Kim > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/