Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755326Ab2ELMEa (ORCPT ); Sat, 12 May 2012 08:04:30 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:38347 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754807Ab2ELME2 (ORCPT ); Sat, 12 May 2012 08:04:28 -0400 Date: Sat, 12 May 2012 05:04:12 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Andrew Morton cc: Christoph Hellwig , Nick Piggin , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 3/10] tmpfs: optimize clearing when writing In-Reply-To: Message-ID: References: User-Agent: Alpine 2.00 (LSU 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2779 Lines: 78 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 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); -- 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/