From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f52.google.com (mail-oi0-f52.google.com [209.85.218.52]) by kanga.kvack.org (Postfix) with ESMTP id A4EF682F64 for ; Thu, 29 Oct 2015 15:13:38 -0400 (EDT) Received: by oifu63 with SMTP id u63so46829896oif.2 for ; Thu, 29 Oct 2015 12:13:38 -0700 (PDT) Received: from mail-oi0-x236.google.com (mail-oi0-x236.google.com. [2607:f8b0:4003:c06::236]) by mx.google.com with ESMTPS id qu7si1974136oeb.68.2015.10.29.12.13.38 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 29 Oct 2015 12:13:38 -0700 (PDT) Received: by oiao187 with SMTP id o187so46505136oia.3 for ; Thu, 29 Oct 2015 12:13:38 -0700 (PDT) Date: Thu, 29 Oct 2015 12:13:35 -0700 (PDT) From: Hugh Dickins Subject: [PATCH] tmpfs: avoid a little creat and stat slowdown Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Josef Bacik , Yu Zhao , Ying Huang , linux-kernel@vger.kernel.org, linux-mm@kvack.org LKP reports that v4.2 commit afa2db2fb6f1 ("tmpfs: truncate prealloc blocks past i_size") causes a 14.5% slowdown in the AIM9 creat-clo benchmark. creat-clo does just what you'd expect from the name, and creat's O_TRUNC on 0-length file does indeed get into more overhead now shmem_setattr() tests "0 <= 0" instead of "0 < 0". I'm not sure how much we care, but I think it would not be too VW-like to add in a check for whether any pages (or swap) are allocated: if none are allocated, there's none to remove from the radix_tree. At first I thought that check would be good enough for the unmaps too, but no: we should not skip the unlikely case of unmapping pages beyond the new EOF, which were COWed from holes which have now been reclaimed, leaving none. This gives me an 8.5% speedup: on Haswell instead of LKP's Westmere, and running a debug config before and after: I hope those account for the lesser speedup. And probably someone has a benchmark where a thousand threads keep on stat'ing the same file repeatedly: forestall that report by adjusting v4.3 commit 44a30220bc0a ("shmem: recalculate file inode when fstat") not to take the spinlock in shmem_getattr() when there's no work to do. Reported-by: Ying Huang Signed-off-by: Hugh Dickins --- mm/shmem.c | 22 ++++++++++++++-------- 1 file changed, 14 insertions(+), 8 deletions(-) --- 4.3-rc7/mm/shmem.c 2015-09-12 18:30:20.857039763 -0700 +++ linux/mm/shmem.c 2015-10-25 11:49:19.931973850 -0700 @@ -548,12 +548,12 @@ static int shmem_getattr(struct vfsmount struct inode *inode = dentry->d_inode; struct shmem_inode_info *info = SHMEM_I(inode); - spin_lock(&info->lock); - shmem_recalc_inode(inode); - spin_unlock(&info->lock); - + if (info->alloced - info->swapped != inode->i_mapping->nrpages) { + spin_lock(&info->lock); + shmem_recalc_inode(inode); + spin_unlock(&info->lock); + } generic_fillattr(inode, stat); - return 0; } @@ -586,10 +586,16 @@ static int shmem_setattr(struct dentry * } if (newsize <= oldsize) { loff_t holebegin = round_up(newsize, PAGE_SIZE); - unmap_mapping_range(inode->i_mapping, holebegin, 0, 1); - shmem_truncate_range(inode, newsize, (loff_t)-1); + if (oldsize > holebegin) + unmap_mapping_range(inode->i_mapping, + holebegin, 0, 1); + if (info->alloced) + shmem_truncate_range(inode, + newsize, (loff_t)-1); /* unmap again to remove racily COWed private pages */ - unmap_mapping_range(inode->i_mapping, holebegin, 0, 1); + if (oldsize > holebegin) + unmap_mapping_range(inode->i_mapping, + holebegin, 0, 1); } } -- 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/ . Don't email: email@kvack.org