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Re: [Qemu-devel] [PATCH 1/2] hw/9pfs: Add new virtfs option cache=writet
From: |
Aneesh Kumar K.V |
Subject: |
Re: [Qemu-devel] [PATCH 1/2] hw/9pfs: Add new virtfs option cache=writethrough to skip host page cache |
Date: |
Wed, 12 Oct 2011 18:49:23 +0530 |
User-agent: |
Notmuch/0.9_rc1-42-g76fdca8 (http://notmuchmail.org) Emacs/23.3.1 (x86_64-pc-linux-gnu) |
On Wed, 12 Oct 2011 10:55:21 +0100, Stefan Hajnoczi <address@hidden> wrote:
> On Mon, Oct 10, 2011 at 10:06 AM, Aneesh Kumar K.V
> <address@hidden> wrote:
> > diff --git a/hw/9pfs/virtio-9p-handle.c b/hw/9pfs/virtio-9p-handle.c
> > index 5c8b5ed..441a37f 100644
> > --- a/hw/9pfs/virtio-9p-handle.c
> > +++ b/hw/9pfs/virtio-9p-handle.c
> > @@ -202,6 +202,15 @@ static ssize_t handle_pwritev(FsContext *ctx, int fd,
> > const struct iovec *iov,
> > return writev(fd, iov, iovcnt);
>
> The sync_file_range(2) call below is dead-code since we'll return
> immediately after writev(2) completes. The writev(2) return value
> needs to be saved temporarily and then returned after
> sync_file_range(2).
Missed that. Will fix in the next update
>
> > }
> > #endif
> > + if (ctx->cache_flags & V9FS_WRITETHROUGH_CACHE) {
>
> -drive cache=writethrough means something different from 9pfs
> "writethrough". This is confusing so I wonder if there is a better
> name like immediate write-out.
>
cache=immediate-write-out ?
> > + /*
> > + * Initiate a writeback. This is not a data integrity sync.
> > + * We want to ensure that we don't leave dirty pages in the cache
> > + * after write when cache=writethrough is sepcified.
> > + */
> > + sync_file_range(fd, offset, 0,
> > + SYNC_FILE_RANGE_WAIT_BEFORE |
> > SYNC_FILE_RANGE_WRITE);
> > + }
>
> I'm not sure whether SYNC_FILE_RANGE_WAIT_BEFORE is necessary. As a
> best-effort mechanism just SYNC_FILE_RANGE_WRITE does the job although
> a client that rapidly rewrites may be able to leave dirty pages in the
> host page cache
Shouldn't we prevent this ? That is the reason for me to use that
WAIT_BEFORE ?
>. SYNC_FILE_RANGE_WAIT_BEFORE ensures that dirty pages
> get written out but it is no longer asynchronous because it blocks.
-aneesh
- [Qemu-devel] [PATCH 1/2] hw/9pfs: Add new virtfs option cache=writethrough to skip host page cache, Aneesh Kumar K.V, 2011/10/07
- [Qemu-devel] [PATCH 2/2] qemu-options.hx: Update virtfs command documentation, Aneesh Kumar K.V, 2011/10/07
- Re: [Qemu-devel] [PATCH 1/2] hw/9pfs: Add new virtfs option cache=writethrough to skip host page cache, Stefan Hajnoczi, 2011/10/08
- Re: [Qemu-devel] [PATCH 1/2] hw/9pfs: Add new virtfs option cache=writethrough to skip host page cache, Aneesh Kumar K.V, 2011/10/09
- Re: [Qemu-devel] [PATCH 1/2] hw/9pfs: Add new virtfs option cache=writethrough to skip host page cache, Stefan Hajnoczi, 2011/10/09
- Re: [Qemu-devel] [PATCH 1/2] hw/9pfs: Add new virtfs option cache=writethrough to skip host page cache, Aneesh Kumar K.V, 2011/10/09
- Re: [Qemu-devel] [PATCH 1/2] hw/9pfs: Add new virtfs option cache=writethrough to skip host page cache, Stefan Hajnoczi, 2011/10/10
- Re: [Qemu-devel] [PATCH 1/2] hw/9pfs: Add new virtfs option cache=writethrough to skip host page cache, Aneesh Kumar K.V, 2011/10/10
- Re: [Qemu-devel] [PATCH 1/2] hw/9pfs: Add new virtfs option cache=writethrough to skip host page cache, Stefan Hajnoczi, 2011/10/12
- Re: [Qemu-devel] [PATCH 1/2] hw/9pfs: Add new virtfs option cache=writethrough to skip host page cache,
Aneesh Kumar K.V <=
- Re: [Qemu-devel] [PATCH 1/2] hw/9pfs: Add new virtfs option cache=writethrough to skip host page cache, Stefan Hajnoczi, 2011/10/12
- Re: [Qemu-devel] [PATCH 1/2] hw/9pfs: Add new virtfs option cache=writethrough to skip host page cache, Aneesh Kumar K.V, 2011/10/12
- Re: [Qemu-devel] [PATCH 1/2] hw/9pfs: Add new virtfs option cache=writethrough to skip host page cache, Stefan Hajnoczi, 2011/10/13