Messages in this thread Patch in this message | | | Date | Wed, 22 Nov 2023 19:35:56 +0800 | Subject | Re: [PATCH v5 6/9] slub: Delay freezing of partial slabs | From | Chengming Zhou <> |
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On 2023/11/22 17:37, Vlastimil Babka wrote: > On 11/20/23 19:49, Mark Brown wrote: >> On Thu, Nov 02, 2023 at 03:23:27AM +0000, chengming.zhou@linux.dev wrote: >>> From: Chengming Zhou <zhouchengming@bytedance.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? >
Great! I manually disabled __CMPXCHG_DOUBLE to reproduce the problem, and this patch can solve the machine hang problem.
BTW, I also did the performance testcase on the machine with 128 CPUs.
stress-ng --rawpkt 128 --rawpkt-ops 100000000
base patched 2.22s 2.35s 2.21s 3.14s 2.19s 4.75s
Found this atomic version performance numbers are not stable.
Should I change back to reuse the slab->__unused (mapcount) field?
Or should we check "s->flags & __CMPXCHG_DOUBLE" in slab_set/clear_node_partial() to avoid using the atomic version?
Thanks!
> ----8<---- > From 000030c1ff055ef6a2ca624d0142f08f3ef19d51 Mon Sep 17 00:00:00 2001 > From: Vlastimil Babka <vbabka@suse.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@suse.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)); > } > > /*
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