Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758483Ab2EOIvX (ORCPT ); Tue, 15 May 2012 04:51:23 -0400 Received: from mail-ob0-f174.google.com ([209.85.214.174]:39874 "EHLO mail-ob0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758434Ab2EOIvR (ORCPT ); Tue, 15 May 2012 04:51:17 -0400 MIME-Version: 1.0 In-Reply-To: References: Date: Tue, 15 May 2012 18:51:16 +1000 Message-ID: Subject: Re: [PATCH 3/10] tmpfs: optimize clearing when writing From: Nick Piggin To: Hugh Dickins Cc: Andrew Morton , Christoph Hellwig , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by nfs id q4F8pUPT009941 Content-Length: 3818 Lines: 79 On 12 May 2012 22:04, Hugh Dickins wrote: > Nick proposed years ago that tmpfs should avoid clearing its pages where > write will overwrite them with new data, as ramfs has long done.  But I > messed it up and just got bad data.  Tried again recently, it works fine. > > Here's time output for writing 4GiB 16 times on this Core i5 laptop: > > before: real    0m21.169s user  0m0.028s sys    0m21.057s >        real    0m21.382s user  0m0.016s sys    0m21.289s >        real    0m21.311s user  0m0.020s sys    0m21.217s > > after:  real    0m18.273s user  0m0.032s sys    0m18.165s >        real    0m18.354s user  0m0.020s sys    0m18.265s >        real    0m18.440s user  0m0.032s sys    0m18.337s > > ramfs:  real    0m16.860s user  0m0.028s sys    0m16.765s >        real    0m17.382s user  0m0.040s sys    0m17.273s >        real    0m17.133s user  0m0.044s sys    0m17.021s Cool, thanks Hugh! Very big speedup. > > Yes, I have done perf reports, but they need more explanation than they > deserve: in summary, clear_page vanishes, its cache loading shifts into > copy_user_generic_unrolled; shmem_getpage_gfp goes down, and surprisingly > mark_page_accessed goes way up - I think because they are respectively > where the cache gets to be reloaded after being purged by clear or copy. > > Suggested-by: Nick Piggin > Signed-off-by: Hugh Dickins > --- >  mm/shmem.c |   20 +++++++++++++++++--- >  1 file changed, 17 insertions(+), 3 deletions(-) > > --- 3045N.orig/mm/shmem.c       2012-05-05 10:46:05.732062006 -0700 > +++ 3045N/mm/shmem.c    2012-05-05 10:46:12.316062172 -0700 > @@ -1095,9 +1095,14 @@ repeat: >                shmem_recalc_inode(inode); >                spin_unlock(&info->lock); > > -               clear_highpage(page); > -               flush_dcache_page(page); > -               SetPageUptodate(page); > +               /* > +                * Let SGP_WRITE caller clear ends if write does not fill page > +                */ > +               if (sgp != SGP_WRITE) { > +                       clear_highpage(page); > +                       flush_dcache_page(page); > +                       SetPageUptodate(page); > +               } >                if (sgp == SGP_DIRTY) >                        set_page_dirty(page); >        } > @@ -1307,6 +1312,14 @@ shmem_write_end(struct file *file, struc >        if (pos + copied > inode->i_size) >                i_size_write(inode, pos + copied); > > +       if (!PageUptodate(page)) { > +               if (copied < PAGE_CACHE_SIZE) { > +                       unsigned from = pos & (PAGE_CACHE_SIZE - 1); > +                       zero_user_segments(page, 0, from, > +                                       from + copied, PAGE_CACHE_SIZE); > +               } > +               SetPageUptodate(page); > +       } >        set_page_dirty(page); >        unlock_page(page); >        page_cache_release(page); > @@ -1768,6 +1781,7 @@ static int shmem_symlink(struct inode *d >                kaddr = kmap_atomic(page); >                memcpy(kaddr, symname, len); >                kunmap_atomic(kaddr); > +               SetPageUptodate(page); >                set_page_dirty(page); >                unlock_page(page); >                page_cache_release(page); ????{.n?+???????+%?????ݶ??w??{.n?+????{??G?????{ay?ʇڙ?,j??f???h?????????z_??(?階?ݢj"???m??????G????????????&???~???iO???z??v?^?m???? ????????I?