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Re: [PATCH v3 5/5] ext4: Defer mmap cmtime update until writeback

To: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Subject: Re: [PATCH v3 5/5] ext4: Defer mmap cmtime update until writeback
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 20 Aug 2013 12:38:49 +1000
Cc: linux-kernel@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, Theodore Ts'o <tytso@xxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx, Jan Kara <jack@xxxxxxx>, Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <d59d6c9790bd3c36b93343ed91be5e0cda7e5f09.1376679411.git.luto@xxxxxxxxxxxxxx>
References: <cover.1376679411.git.luto@xxxxxxxxxxxxxx> <d59d6c9790bd3c36b93343ed91be5e0cda7e5f09.1376679411.git.luto@xxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Fri, Aug 16, 2013 at 04:22:12PM -0700, Andy Lutomirski wrote:
> A fancier implementation could probably avoid an extra journal
> transaction by adding a mapping_test_clear_cmtime call in
> ext4_writepages, but this should already be a considerable
> improvement -- we'll start one transaction per writepages call
> instead of one per page.

I'd like to see more than just an ext4 implementation - btrfs and
XFS are the other main filesystems that should behave identically.

Also, it's worthwhile to write a generic xfstest to ensure that they
all update the timestamp appropriately - if its' in xfstests, then
we can basically guarantee that it won't get randomly regressed in
future, and other filesystems can be easily verified as well sa
their implement this.


Dave Chinner

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