linux-kernel - Re: [PATCH 1/1] mm/page_alloc: Leave IRQs enabled for per-cpu page allocations

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Message-ID: <20220825091051.7awtjp25yh7bv3xf@techsingularity.net>
Date:   Thu, 25 Aug 2022 10:11:19 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Yu Zhao <yuzhao@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Nicolas Saenz Julienne <nsaenzju@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...nel.org>,
        Hugh Dickins <hughd@...gle.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH 1/1] mm/page_alloc: Leave IRQs enabled for per-cpu page
 allocations

On Wed, Aug 24, 2022 at 10:58:26PM -0600, Yu Zhao wrote:
> On Wed, Aug 24, 2022 at 8:18 AM Mel Gorman <mgorman@...hsingularity.net> wrote:
> >
> > The pcp_spin_lock_irqsave protecting the PCP lists is IRQ-safe as a task
> > allocating from the PCP must not re-enter the allocator from IRQ context.
> > In each instance where IRQ-reentrancy is possible, the lock is acquired using
> > pcp_spin_trylock_irqsave() even though IRQs are disabled and re-entrancy
> > is impossible.
> >
> > Demote the lock to pcp_spin_lock avoids an IRQ disable/enable in the common
> > case at the cost of some IRQ allocations taking a slower path. If the PCP
> > lists need to be refilled, the zone lock still needs to disable IRQs but
> > that will only happen on PCP refill and drain. If an IRQ is raised when
> > a PCP allocation is in progress, the trylock will fail and fallback to
> > using the buddy lists directly. Note that this may not be a universal win
> > if an interrupt-intensive workload also allocates heavily from interrupt
> > context and contends heavily on the zone->lock as a result.
> 
> Hi,
> 
> This patch caused the following warning. Please take a look.
> 

Thanks. I see the patch is already taken out of mm-unstable so back to
the drawing board!

-- 
Mel Gorman
SUSE Labs