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From: Paolo Bonzini <pbonzini@redhat.com>
To: Chris Mason <clm@fb.com>, Boris Burkov <boris@bur.io>
Cc: Sean Christopherson <seanjc@google.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Kernel Team <Kernel-team@fb.com>
Subject: Re: [PATCH] KVM: use set_page_dirty rather than SetPageDirty
Date: Thu, 27 Jan 2022 13:20:23 +0100	[thread overview]
Message-ID: <3f4efc3d-f351-0fcb-e231-b422ea262f66@redhat.com> (raw)
In-Reply-To: <3876CE62-6E66-4CCE-ADED-69010EA72394@fb.com>

On 1/27/22 01:02, Chris Mason wrote:
> From the btrfs side, bare calls to set_page_dirty() are suboptimal,
> since it doesn’t go through the ->page_mkwrite() dance that we use to
> properly COW things.  It’s still much better than SetPageDirty(), but
> I’d love to understand why kvm needs to dirty the page so we can
> figure out how to go through the normal mmap file io paths.
Shouldn't ->page_mkwrite() occur at the point of get_user_pages, such as 
via handle_mm_fault->handle_pte_fault->do_fault->do_shared_fault?  That 
always happens before SetPageDirty(), or set_page_dirty() after Boris's 
patch.

Thanks,

Paolo


  parent reply	other threads:[~2022-01-27 12:20 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-26 19:54 [PATCH] KVM: use set_page_dirty rather than SetPageDirty Boris Burkov
2022-01-26 21:59 ` Sean Christopherson
2022-01-26 23:11   ` Boris Burkov
2022-01-27  0:02     ` Chris Mason
2022-01-27  1:36       ` Sean Christopherson
2022-01-27 15:00         ` Chris Mason
2022-01-27 12:20       ` Paolo Bonzini [this message]
2022-01-27 14:52         ` Chris Mason

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