linux-kernel - Re: [PATCH v2 2/6] mm: handle swap page faults under VMA lock if page is uncontended

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Message-ID: <ZIcktx8DPYxtV2Sd@x1n>
Date:   Mon, 12 Jun 2023 09:59:19 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     Matthew Wilcox <willy@...radead.org>, akpm@...ux-foundation.org,
        hannes@...xchg.org, mhocko@...e.com, josef@...icpanda.com,
        jack@...e.cz, ldufour@...ux.ibm.com, laurent.dufour@...ibm.com,
        michel@...pinasse.org, liam.howlett@...cle.com, jglisse@...gle.com,
        vbabka@...e.cz, minchan@...gle.com, dave@...olabs.net,
        punit.agrawal@...edance.com, lstoakes@...il.com, hdanton@...a.com,
        apopple@...dia.com, ying.huang@...el.com, david@...hat.com,
        yuzhao@...gle.com, dhowells@...hat.com, hughd@...gle.com,
        viro@...iv.linux.org.uk, brauner@...nel.org,
        pasha.tatashin@...een.com, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...roid.com
Subject: Re: [PATCH v2 2/6] mm: handle swap page faults under VMA lock if
 page is uncontended

On Fri, Jun 09, 2023 at 03:34:34PM -0700, Suren Baghdasaryan wrote:
> On Fri, Jun 9, 2023 at 1:45 PM Peter Xu <peterx@...hat.com> wrote:
> >
> > On Fri, Jun 09, 2023 at 09:35:49PM +0100, Matthew Wilcox wrote:
> > > On Fri, Jun 09, 2023 at 04:25:42PM -0400, Peter Xu wrote:
> > > > >  bool __folio_lock_or_retry(struct folio *folio, struct mm_struct *mm,
> > > > >                    unsigned int flags)
> > > > >  {
> > > > > + /* Can't do this if not holding mmap_lock */
> > > > > + if (flags & FAULT_FLAG_VMA_LOCK)
> > > > > +         return false;
> > > >
> > > > If here what we need is the page lock, can we just conditionally release
> > > > either mmap lock or vma lock depending on FAULT_FLAG_VMA_LOCK?
> > >
> > > See patch 5 ...
> >
> > Just reaching.. :)
> >
> > Why not in one shot, then?
> 
> I like small incremental changes, but I can squash them if that helps
> in having a complete picture.

Yes that'll be appreciated.  IMHO keeping changing semantics of
FAULT_FLAG_VMA_LOCK for the folio lock function in the same small series is
confusing.

-- 
Peter Xu