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Re: [Qemu-devel] [PATCH v2 6/8] migration: move handle of zero page to t


From: Peter Xu
Subject: Re: [Qemu-devel] [PATCH v2 6/8] migration: move handle of zero page to the thread
Date: Mon, 23 Jul 2018 17:40:21 +0800
User-agent: Mutt/1.10.0 (2018-05-17)

On Mon, Jul 23, 2018 at 04:44:49PM +0800, Xiao Guangrong wrote:

[...]

> > > 
> > > However, it is not safe to do ram_release_pages in the thread as it's
> > > not protected it multithreads. Fortunately, compression will be disabled
> > > if it switches to post-copy, so i preferred to keep current behavior and
> > > deferred to fix it after this patchset has been merged.
> > 
> > Do you mean ram_release_pages() is not thread-safe?  Why?  I didn't
> > notice it before but I feel like it is safe.
> 
> bitmap_clear() called in the function is not safe.

Yeah, and the funny thing is that I don't think ram_release_pages()
should even touch the receivedmap...  It's possible that the
release-ram feature for postcopy is broken.

Never mind on that.  I'll post a patch to fix it, then I think the
ram_release_pages() will be thread safe.

Then this patch shouldn't be affected and it should be fine after that
fix.

Regards,

-- 
Peter Xu



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