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

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Message-ID: <CAJuCfpFSYG3cTxP+B4XrWY2=jGd3fdEG6h-kb0G4R8n9DGtwcQ@mail.gmail.com>
Date: Wed, 26 Feb 2025 10:59:01 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Matthew Wilcox <willy@...radead.org>
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 8:22 AM Suren Baghdasaryan <surenb@...gle.com> wrote:
>
> On Wed, Feb 26, 2025 at 8:16 AM Matthew Wilcox <willy@...radead.org> wrote:
> >
> > 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.
>
> Ack.

I posted v2 at https://lore.kernel.org/all/20250226185510.2732648-2-surenb@google.com/
as part of a pachset which includes the fix for PTE unmapping that
Peter reported. Patchset is rebased over mm-hotfixes-unstable which
includes Barry's fix to the nearby code. This avoids merge conflicts.