linux-kernel - Re: [PATCH v5 6/9] slub: Delay freezing of partial slabs

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Message-ID: <83ff4b9e-94f1-8b35-1233-3dd414ea4dfe@suse.cz>
Date:   Wed, 22 Nov 2023 10:37:39 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Mark Brown <broonie@...nel.org>, chengming.zhou@...ux.dev
Cc:     cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org,
        roman.gushchin@...ux.dev, 42.hyeyoo@...il.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Chengming Zhou <zhouchengming@...edance.com>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v5 6/9] slub: Delay freezing of partial slabs

On 11/20/23 19:49, Mark Brown wrote:
> On Thu, Nov 02, 2023 at 03:23:27AM +0000, chengming.zhou@...ux.dev wrote:
>> From: Chengming Zhou <zhouchengming@...edance.com>
>> 
>> Now we will freeze slabs when moving them out of node partial list to
>> cpu partial list, this method needs two cmpxchg_double operations:
>> 
>> 1. freeze slab (acquire_slab()) under the node list_lock
>> 2. get_freelist() when pick used in ___slab_alloc()
> 
> Recently -next has been failing to boot on a Raspberry Pi 3 with an arm
> multi_v7_defconfig and a NFS rootfs, a bisect appears to point to this
> patch (in -next as c8d312e039030edab25836a326bcaeb2a3d4db14) as having
> introduced the issue.  I've included the full bisect log below.
> 
> When we see problems we see RCU stalls while logging in, for example:

Can you try this, please?

----8<----
>From 000030c1ff055ef6a2ca624d0142f08f3ef19d51 Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <vbabka@...e.cz>
Date: Wed, 22 Nov 2023 10:32:41 +0100
Subject: [PATCH] mm/slub: try to fix hangs without cmpxchg64/128

If we don't have cmpxchg64/128 and resort to slab_lock()/slab_unlock()
which uses PG_locked, we can get RMW with the newly introduced
slab_set/clear_node_partial() operation that modify PG_workingset so all
the operations have to be atomic now.

Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/slub.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index bcb5b2c4e213..f2cdb81ab02e 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -522,7 +522,7 @@ static __always_inline void slab_unlock(struct slab *slab)
 	struct page *page = slab_page(slab);
 
 	VM_BUG_ON_PAGE(PageTail(page), page);
-	__bit_spin_unlock(PG_locked, &page->flags);
+	bit_spin_unlock(PG_locked, &page->flags);
 }
 
 static inline bool
@@ -2127,12 +2127,12 @@ static inline bool slab_test_node_partial(const struct slab *slab)
 
 static inline void slab_set_node_partial(struct slab *slab)
 {
-	__set_bit(PG_workingset, folio_flags(slab_folio(slab), 0));
+	set_bit(PG_workingset, folio_flags(slab_folio(slab), 0));
 }
 
 static inline void slab_clear_node_partial(struct slab *slab)
 {
-	__clear_bit(PG_workingset, folio_flags(slab_folio(slab), 0));
+	clear_bit(PG_workingset, folio_flags(slab_folio(slab), 0));
 }
 
 /*
-- 
2.42.1