linux-kernel - Re: [PATCH 1/1] userfaultfd: do not block on locking a large folio with raised refcount

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Message-ID: <Z78-YdCGtbV61x_Z@casper.infradead.org>
Date: Wed, 26 Feb 2025 16:16:33 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>, akpm@...ux-foundation.org,
	lokeshgidra@...gle.com, aarcange@...hat.com, 21cnbao@...il.com,
	v-songbaohua@...o.com, david@...hat.com, peterx@...hat.com,
	lorenzo.stoakes@...cle.com, hughd@...gle.com, jannh@...gle.com,
	kaleshsingh@...gle.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] userfaultfd: do not block on locking a large folio
 with raised refcount

On Wed, Feb 26, 2025 at 08:11:25AM -0800, Suren Baghdasaryan wrote:
> On Wed, Feb 26, 2025 at 6:59 AM Liam R. Howlett <Liam.Howlett@...cle.com> wrote:
> > Reversing the locking/folio_get() is okay because of the src_ptl spin
> > lock, right?  It might be worth saying something about it in the
> > comment?
> 
> That is correct. We take both folio lock and refcount before we drop
> PTL. I'll add a comment. Thanks!

In the commit message, not in the code, please.