lkml.org 
[lkml]   [2022]   [Jun]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH 7/7] mm/page_alloc: Replace local_lock with normal spinlock
    From
    Date
    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

    \
     
     \ /
      Last update: 2022-06-21 11:32    [W:2.541 / U:0.016 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site