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Re: [Qemu-devel] [PATCH 25/27] block/parallels: add prealloc-mode and pr
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH 25/27] block/parallels: add prealloc-mode and prealloc-size open paramemets |
Date: |
Mon, 18 May 2015 17:32:43 +0100 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Tue, Apr 28, 2015 at 10:46:58AM +0300, Denis V. Lunev wrote:
> This is preparational commit for tweaks in Parallels image expansion.
> The idea is that enlarge via truncate by one data block is slow. It
> would be much better to use fallocate via bdrv_write_zeroes and
> expand by some significant amount at once.
>
> Original idea with sequential file writing to the end of the file without
> fallocate/truncate would be slower than this approach if the image is
> expanded with several operations:
> - each image expanding means file metadata update, i.e. filesystem
> journal write. Truncate/write to newly truncated space update file
> metadata twice thus truncate removal helps. With fallocate call
> inside bdrv_write_zeroes file metadata is updated only once and
> this should happen infrequently thus this approach is the best one
> for the image expansion
> - tail writes are ordered, i.e. the guest IO queue could not be sent
> immediately to the host introducing additional IO delays
>
> This patch just adds proper parameters into BDRVParallelsState and
> performs options parsing in parallels_open.
>
> Signed-off-by: Denis V. Lunev <address@hidden>
> CC: Roman Kagan <address@hidden>
> CC: Kevin Wolf <address@hidden>
> CC: Stefan Hajnoczi <address@hidden>
> ---
> block/parallels.c | 83
> +++++++++++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 77 insertions(+), 6 deletions(-)
Reviewed-by: Stefan Hajnoczi <address@hidden>
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Stefan Hajnoczi <=