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Re: [Qemu-devel] [PATCH 7/7] block/raw-posix: set max_write_zeroes to IN
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [PATCH 7/7] block/raw-posix: set max_write_zeroes to INT_MAX for regular files |
Date: |
Mon, 2 Feb 2015 14:23:55 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
Am 30.01.2015 um 09:42 hat Denis V. Lunev geschrieben:
> fallocate() works fine and could handle properly with arbitrary size
> requests. There is no sense to reduce the amount of space to fallocate.
> The bigger is the size, the better is the performance as the amount of
> journal updates is reduced.
>
> The patch changes behavior for both generic filesystem and XFS codepaths,
> which are different in handle_aiocb_write_zeroes. The implementation
> of fallocate and xfsctl(XFS_IOC_ZERO_RANGE) for XFS are exactly the same
> thus the change is fine for both ways.
>
> Signed-off-by: Denis V. Lunev <address@hidden>
> Reviewed-by: Max Reitz <address@hidden>
> CC: Kevin Wolf <address@hidden>
> CC: Stefan Hajnoczi <address@hidden>
> CC: Peter Lieven <address@hidden>
> CC: Fam Zheng <address@hidden>
> ---
> block/raw-posix.c | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
> diff --git a/block/raw-posix.c b/block/raw-posix.c
> index 7b42f37..933c778 100644
> --- a/block/raw-posix.c
> +++ b/block/raw-posix.c
> @@ -293,6 +293,20 @@ static void raw_probe_alignment(BlockDriverState *bs,
> int fd, Error **errp)
> }
> }
>
> +static void raw_probe_max_write_zeroes(BlockDriverState *bs)
> +{
> + BDRVRawState *s = bs->opaque;
> + struct stat st;
> +
> + if (fstat(s->fd, &st) < 0) {
> + return; /* no problem, keep default value */
> + }
> + if (!S_ISREG(st.st_mode) || !s->discard_zeroes) {
> + return;
> + }
> + bs->bl.max_write_zeroes = INT_MAX;
> +}
Peter, do you remember why INT_MAX isn't actually the default? I think
the most reasonable behaviour would be that a limitation is only used if
a block driver requests it, and otherwise unlimited is assumed.
We can take this patch to raw-posix, it is certainly not wrong. But any
format driver or filter will still, in most cases needlessly, apply
MAX_WRITE_ZEROES_DEFAULT, i.e. a 16 MB maximum, so I think we should
consider making a change to the default.
Kevin
- Re: [Qemu-devel] [PATCH 7/7] block/raw-posix: set max_write_zeroes to INT_MAX for regular files,
Kevin Wolf <=
- Re: [Qemu-devel] [PATCH 7/7] block/raw-posix: set max_write_zeroes to INT_MAX for regular files, Peter Lieven, 2015/02/02
- Re: [Qemu-devel] [PATCH 7/7] block/raw-posix: set max_write_zeroes to INT_MAX for regular files, Kevin Wolf, 2015/02/02
- Re: [Qemu-devel] [PATCH 7/7] block/raw-posix: set max_write_zeroes to INT_MAX for regular files, Peter Lieven, 2015/02/02
- Re: [Qemu-devel] [PATCH 7/7] block/raw-posix: set max_write_zeroes to INT_MAX for regular files, Kevin Wolf, 2015/02/02
- Re: [Qemu-devel] [PATCH 7/7] block/raw-posix: set max_write_zeroes to INT_MAX for regular files, Peter Lieven, 2015/02/02
- Re: [Qemu-devel] [PATCH 7/7] block/raw-posix: set max_write_zeroes to INT_MAX for regular files, Denis V. Lunev, 2015/02/02
- Re: [Qemu-devel] [PATCH 7/7] block/raw-posix: set max_write_zeroes to INT_MAX for regular files, Kevin Wolf, 2015/02/02
- Re: [Qemu-devel] [PATCH 7/7] block/raw-posix: set max_write_zeroes to INT_MAX for regular files, Denis V. Lunev, 2015/02/02