From: Nicolas Saenz Julienne <nsaenzju@redhat.com>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Marcelo Tosatti <mtosatti@redhat.com>,
Vlastimil Babka <vbabka@suse.cz>,
Michal Hocko <mhocko@kernel.org>, Hugh Dickins <hughd@google.com>,
LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>
Subject: Re: [PATCH 7/7] mm/page_alloc: Replace local_lock with normal spinlock
Date: Tue, 21 Jun 2022 11:31:41 +0200 [thread overview]
Message-ID: <c00a1b621850fedaea3da01ab178e91b79f1dce5.camel@redhat.com> (raw)
In-Reply-To: <20220621092950.GF15453@techsingularity.net>
On Tue, 2022-06-21 at 10:29 +0100, Mel Gorman wrote:
> On Fri, Jun 17, 2022 at 11:39:03AM +0200, Nicolas Saenz Julienne wrote:
> > Hi Mel,
> >
> > On Mon, 2022-06-13 at 13:56 +0100, Mel Gorman wrote:
> > > @@ -3446,12 +3490,16 @@ void free_unref_page(struct page *page, unsigned int order)
> > > migratetype = MIGRATE_MOVABLE;
> > > }
> > >
> > > - local_lock_irqsave(&pagesets.lock, flags);
> > > - freed_pcp = free_unref_page_commit(page, migratetype, order, false);
> > > - local_unlock_irqrestore(&pagesets.lock, flags);
> > > -
> > > - if (unlikely(!freed_pcp))
> > > + zone = page_zone(page);
> > > + pcp_trylock_prepare(UP_flags);
> >
> > Now that you're calling the *_irqsave() family of function you can drop
> > pcp_trylock_prepare/finish()
> >
> > For the record in UP:
> >
> > #define spin_trylock_irqsave(lock, flags) \
> > ({ \
> > local_irq_save(flags); \
> > 1;
> > })
> >
>
> The missing patch that is deferred for a later release uses spin_trylock
> so unless that is never merged because there is an unfixable flaw in it,
> I'd prefer to leave the preparation in place.
>
> > > + pcp = pcpu_spin_trylock_irqsave(struct per_cpu_pages, lock, zone->per_cpu_pageset, flags);
> > > + if (pcp) {
> > > + free_unref_page_commit(pcp, zone, page, migratetype, order);
> > > + pcp_spin_unlock_irqrestore(pcp, flags);
> > > + } else {
> > > free_one_page(page_zone(page), page, pfn, order, migratetype, FPI_NONE);
> > > + }
> > > + pcp_trylock_finish(UP_flags);
> > > }
> > >
> > > /*
> >
> > As Vlastimil mentioned elsewhere, I also wonder if it makes sense to just
> > bypass patch #5. Especially as its intent isn't true anymore:
> >
> > "As preparation for dealing with both of those problems, protect the lists
> > with a spinlock. The IRQ-unsafe version of the lock is used because IRQs
> > are already disabled by local_lock_irqsave. spin_trylock is used in
> > preparation for a time when local_lock could be used instead of
> > lock_lock_irqsave."
> >
>
> It's still true, the patch just isn't included as I wanted them to be
> separated by time so a bisection that points to it is "obvious" instead
> of pointing at the whole series as being a potential problem.
Understood, I jumped straight into the code and missed your comment in the
cover letter.
Thanks!
--
Nicolás Sáenz
next prev parent reply other threads:[~2022-06-21 9:31 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-13 12:56 [PATCH v4 00/7] Drain remote per-cpu directly Mel Gorman
2022-06-13 12:56 ` [PATCH 1/7] mm/page_alloc: Add page->buddy_list and page->pcp_list Mel Gorman
2022-06-13 12:56 ` [PATCH 2/7] mm/page_alloc: Use only one PCP list for THP-sized allocations Mel Gorman
2022-06-13 12:56 ` [PATCH 3/7] mm/page_alloc: Split out buddy removal code from rmqueue into separate helper Mel Gorman
2022-06-13 12:56 ` [PATCH 4/7] mm/page_alloc: Remove mistaken page == NULL check in rmqueue Mel Gorman
2022-06-13 12:56 ` [PATCH 5/7] mm/page_alloc: Protect PCP lists with a spinlock Mel Gorman
2022-06-16 15:59 ` Vlastimil Babka
2022-06-13 12:56 ` [PATCH 6/7] mm/page_alloc: Remotely drain per-cpu lists Mel Gorman
2022-06-16 16:41 ` Vlastimil Babka
2022-06-13 12:56 ` [PATCH 7/7] mm/page_alloc: Replace local_lock with normal spinlock Mel Gorman
2022-06-15 22:43 ` Yu Zhao
[not found] ` <CGME20220615224855eucas1p1ea6d90c23ec9423dfe04b267f6dddd2a@eucas1p1.samsung.com>
2022-06-15 22:48 ` Marek Szyprowski
2022-06-15 23:04 ` Andrew Morton
2022-06-16 3:05 ` Yu Zhao
2022-06-17 7:55 ` Vlastimil Babka
2022-06-17 6:47 ` Marek Szyprowski
2022-06-21 9:21 ` Mel Gorman
2022-06-16 17:01 ` Vlastimil Babka
2022-06-16 21:07 ` Yu Zhao
2022-06-17 7:57 ` Vlastimil Babka
2022-06-21 9:27 ` Mel Gorman
2022-06-21 9:26 ` Mel Gorman
2022-06-17 9:39 ` Nicolas Saenz Julienne
2022-06-21 9:29 ` Mel Gorman
2022-06-21 9:31 ` Nicolas Saenz Julienne [this message]
2022-07-03 9:44 ` [mm/page_alloc] 2bd8eec68f: BUG:sleeping_function_called_from_invalid_context_at_mm/gup.c kernel test robot
2022-07-03 20:22 ` Andrew Morton
2022-07-05 13:51 ` Oliver Sang
2022-07-06 9:55 ` Mel Gorman
2022-07-06 11:53 ` Mel Gorman
2022-07-06 14:21 ` Oliver Sang
2022-07-06 14:52 ` Mel Gorman
2022-07-07 8:22 ` Oliver Sang
2022-07-06 14:25 ` Oliver Sang
2022-07-06 14:53 ` Mel Gorman
2022-07-07 21:55 ` Vlastimil Babka
2022-07-08 10:56 ` Mel Gorman
2022-07-12 5:04 ` Oliver Sang
2022-06-24 12:54 [PATCH v5 00/7] Drain remote per-cpu directly Mel Gorman
2022-06-24 12:54 ` [PATCH 7/7] mm/page_alloc: Replace local_lock with normal spinlock Mel Gorman
2022-06-24 18:59 ` Yu Zhao
2022-07-04 14:39 ` Vlastimil Babka
2022-07-04 16:33 ` Nicolas Saenz Julienne
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