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: <ZIONJQGuhYiDnFdg@casper.infradead.org>
Date:   Fri, 9 Jun 2023 21:35:49 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Peter Xu <peterx@...hat.com>
Cc:     Suren Baghdasaryan <surenb@...gle.com>, 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 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 ...