From: Mike Galbraith <efault@gmx.de>
To: Vlastimil Babka <vbabka@suse.cz>,
Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>
Cc: linux-rt-users@vger.kernel.org,
Mel Gorman <mgorman@techsingularity.net>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: Re: [rfc/patch] mm/slub: restore/expand unfreeze_partials() local exclusion scope
Date: Tue, 27 Jul 2021 06:09:10 +0200 [thread overview]
Message-ID: <7970e9c3de5d29b93f692001a3796da1b3df45b4.camel@gmx.de> (raw)
In-Reply-To: <26c181c9-ec48-09e2-2d73-6fc769a19c76@suse.cz>
On Mon, 2021-07-26 at 23:26 +0200, Vlastimil Babka wrote:
> On 7/26/21 7:00 PM, Mike Galbraith wrote:
> >
> > Why not do something like the below?...
>
> Yep, sounds like a good approach, thanks. Percpu partial is not *the*
> SLUB fast path, so it should be sufficient without the lockless cmpxchg
> tricks. Will incorporate in updated series.
Great, my >= 5.13 trees will meanwhile wear it like so:
From: Vlastimil Babka <vbabka@suse.cz>
Date: Fri, 23 Jul 2021 23:17:18 +0200
mm, slub: Fix PREEMPT_RT plus SLUB_CPU_PARTIAL local exclusion
See https://lkml.org/lkml/2021/7/25/185
Mike: Remove ifdefs, make all configs take the straight line path layed
out for RT by Vlastimil in his prospective (now confirmed) fix.
Signed-off-by: Mike Galbraith <efault@gmx.de>
---
mm/slub.c | 79 ++++++++++++++++++++++++++++++++------------------------------
1 file changed, 41 insertions(+), 38 deletions(-)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2437,13 +2437,12 @@ static void __unfreeze_partials(struct k
static void unfreeze_partials(struct kmem_cache *s)
{
struct page *partial_page;
+ unsigned long flags;
- do {
- partial_page = this_cpu_read(s->cpu_slab->partial);
-
- } while (partial_page &&
- this_cpu_cmpxchg(s->cpu_slab->partial, partial_page, NULL)
- != partial_page);
+ local_lock_irqsave(&s->cpu_slab->lock, flags);
+ partial_page = this_cpu_read(s->cpu_slab->partial);
+ this_cpu_write(s->cpu_slab->partial, NULL);
+ local_unlock_irqrestore(&s->cpu_slab->lock, flags);
if (partial_page)
__unfreeze_partials(s, partial_page);
@@ -2480,41 +2479,45 @@ static void put_cpu_partial(struct kmem_
{
#ifdef CONFIG_SLUB_CPU_PARTIAL
struct page *oldpage;
- int pages;
- int pobjects;
-
- slub_get_cpu_ptr(s->cpu_slab);
- do {
- pages = 0;
- pobjects = 0;
- oldpage = this_cpu_read(s->cpu_slab->partial);
-
- if (oldpage) {
- pobjects = oldpage->pobjects;
- pages = oldpage->pages;
- if (drain && pobjects > slub_cpu_partial(s)) {
- /*
- * partial array is full. Move the existing
- * set to the per node partial list.
- */
- unfreeze_partials(s);
- oldpage = NULL;
- pobjects = 0;
- pages = 0;
- stat(s, CPU_PARTIAL_DRAIN);
- }
+ struct page *page_to_unfreeze = NULL;
+ unsigned long flags;
+ int pages = 0, pobjects = 0;
+
+ local_lock_irqsave(&s->cpu_slab->lock, flags);
+
+ if (oldpage = this_cpu_read(s->cpu_slab->partial)) {
+ pobjects = oldpage->pobjects;
+ pages = oldpage->pages;
+ if (drain && pobjects > slub_cpu_partial(s)) {
+ /*
+ * partial array is full. Move the existing
+ * set to the per node partial list.
+ *
+ * Postpone unfreezing until we drop the local
+ * lock to avoid an RT unlock/relock requirement
+ * due to MEMCG __slab_free() recursion.
+ */
+ page_to_unfreeze = oldpage;
+
+ oldpage = NULL;
+ pobjects = 0;
+ pages = 0;
+ stat(s, CPU_PARTIAL_DRAIN);
}
+ }
+
+ pages++;
+ pobjects += page->objects - page->inuse;
+
+ page->pages = pages;
+ page->pobjects = pobjects;
+ page->next = oldpage;
- pages++;
- pobjects += page->objects - page->inuse;
+ this_cpu_write(s->cpu_slab->partial, page);
+ local_unlock_irqrestore(&s->cpu_slab->lock, flags);
- page->pages = pages;
- page->pobjects = pobjects;
- page->next = oldpage;
-
- } while (this_cpu_cmpxchg(s->cpu_slab->partial, oldpage, page)
- != oldpage);
- slub_put_cpu_ptr(s->cpu_slab);
+ if (page_to_unfreeze)
+ __unfreeze_partials(s, page_to_unfreeze);
#endif /* CONFIG_SLUB_CPU_PARTIAL */
}
next prev parent reply other threads:[~2021-07-27 4:09 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-08 9:42 [ANNOUNCE] v5.13-rt1 Thomas Gleixner
2021-07-09 5:20 ` [patch] mm/slub: Fix kmem_cache_alloc_bulk() error path Mike Galbraith
2021-07-09 5:20 ` [patch] mm/slub: Replace do_slab_free() local_lock_irqsave/restore() calls in PREEMPT_RT scope Mike Galbraith
2021-07-09 5:21 ` [rfc/patch] mm/slub: restore/expand unfreeze_partials() local exclusion scope Mike Galbraith
2021-07-09 5:25 ` Mike Galbraith
2021-07-09 19:28 ` Thomas Gleixner
2021-07-10 1:12 ` Mike Galbraith
2021-07-15 16:34 ` Mike Galbraith
2021-07-17 14:58 ` [patch] v2 " Mike Galbraith
2021-07-18 7:58 ` Vlastimil Babka
2021-07-18 8:11 ` Mike Galbraith
2021-07-18 15:43 ` Mike Galbraith
2021-07-18 21:19 ` Vlastimil Babka
2021-07-19 4:01 ` Mike Galbraith
2021-07-19 13:15 ` Mike Galbraith
2021-07-20 2:46 ` kernel test robot
2021-07-20 8:56 ` [rfc/patch] " Vlastimil Babka
2021-07-20 11:26 ` Mike Galbraith
2021-07-21 4:56 ` Mike Galbraith
2021-07-21 8:44 ` Vlastimil Babka
2021-07-21 9:33 ` Mike Galbraith
2021-07-23 22:39 ` Vlastimil Babka
2021-07-24 2:25 ` Mike Galbraith
2021-07-25 14:09 ` Mike Galbraith
2021-07-25 14:16 ` Vlastimil Babka
2021-07-25 15:02 ` Mike Galbraith
2021-07-25 16:27 ` Vlastimil Babka
2021-07-25 19:12 ` Vlastimil Babka
2021-07-25 19:34 ` Vlastimil Babka
2021-07-26 10:04 ` Mike Galbraith
2021-07-26 17:00 ` Mike Galbraith
2021-07-26 21:26 ` Vlastimil Babka
2021-07-27 4:09 ` Mike Galbraith [this message]
2021-07-28 16:59 ` Vlastimil Babka
2021-07-29 4:51 ` Mike Galbraith
2021-07-29 9:51 ` Vlastimil Babka
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