linux-kernel - Re: [PATCH 2/2] msync: start async writeout when MS

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Message-ID: <4FD9D813.1010203@redhat.com>
Date:	Thu, 14 Jun 2012 14:24:51 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	linux-kernel@...r.kernel.org, Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH 2/2] msync: start async writeout when MS_ASYNC

Il 13/06/2012 23:29, Andrew Morton ha scritto:
> Also, it hardwires into the kernel behaviour which userspace itself
> could have initiated, with sync_file_range().  ie: reduced flexibility.

Actually sync_file_range calls filemap_fdatawrite_range with
WB_SYNC_ALL, hence it does the writeout synchronously and can block for
an extended period of time.  Hence sync_file_range is more similar to
MS_SYNC except without the metadata write.

Instead, this patch uses WB_SYNC_NONE, while still using tag-and-write
to avoid livelock.

I'll wait a day or two to let others voice their opinions, and then send
a fixed v2 with updated commit messages from this discussion.

Paolo
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