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Re: [Qemu-devel] [RFC 2/2] block/file-posix: verify page cache is not us
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [RFC 2/2] block/file-posix: verify page cache is not used |
Date: |
Fri, 20 Apr 2018 11:02:21 +0800 |
User-agent: |
Mutt/1.9.2 (2017-12-15) |
On Thu, Apr 19, 2018 at 10:05:47AM +0100, Dr. David Alan Gilbert wrote:
> * Stefan Hajnoczi (address@hidden) wrote:
> > This commit is for debugging only. Do not merge it.
> >
> > mincore(2) checks whether pages are resident. Use it to verify that
> > page cache has been dropped.
> >
> > You can trigger a verification failure by mmapping the image file from
> > another process and loading a byte from a page so that it becomes
> > resident. bdrv_co_invalidate_cache() will fail while the process is
> > alive.
>
> It doesn't seem a bad diagnostic to keep in (with a switch to activate)
> for when we're faced with some weird corruption on some weird storage
> system.
Okay. It's very slow to mmap an entire image file and query mincore(2)
so it needs to be off by default.
Stefan
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- [Qemu-devel] [RFC 1/2] block/file-posix: implement bdrv_co_invalidate_cache() on Linux, (continued)
[Qemu-devel] [RFC 2/2] block/file-posix: verify page cache is not used, Stefan Hajnoczi, 2018/04/19
Re: [Qemu-devel] [RFC 0/2] block/file-posix: allow -drive cache.direct=off live migration, Eric Blake, 2018/04/19