From: Matthew Wilcox <willy@infradead.org>
To: Ryan Roberts <ryan.roberts@arm.com>
Cc: Zi Yan <ziy@nvidia.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, Yang Shi <shy828301@gmail.com>,
Huang Ying <ying.huang@intel.com>
Subject: Re: [PATCH v3 10/18] mm: Allow non-hugetlb large folios to be batch processed
Date: Fri, 8 Mar 2024 15:33:30 +0000 [thread overview]
Message-ID: <ZesvyqgqE_B9MDlT@casper.infradead.org> (raw)
In-Reply-To: <7415b36c-b5d3-4655-92e1-b303104bf4a9@arm.com>
On Fri, Mar 08, 2024 at 12:09:38PM +0000, Ryan Roberts wrote:
> On 08/03/2024 11:44, Ryan Roberts wrote:
> > Dumping all the CPU back traces with gdb, all the cores (except one) are
> > contending on the the deferred split lock.
> >
> > A couple of thoughts:
> >
> > - Since we are now taking a maximum of 15 folios into a batch,
> > deferred_split_scan() is called much more often (in a tight loop from
> > do_shrink_slab()). Could it be that we are just trying to take the lock so much
> > more often now? I don't think it's quite that simple because we take the lock
> > for every single folio when adding it to the queue, so the dequeing cost should
> > still be a factor of 15 locks less.
> >
> > - do_shrink_slab() might be calling deferred_split_scan() in a tight loop with
> > deferred_split_scan() returning 0 most of the time. If there are still folios on
> > the deferred split list but deferred_split_scan() was unable to lock any folios
> > then it will return 0, not SHRINK_STOP, so do_shrink_slab() will keep calling
> > it, essentially live locking. Has your patch changed the duration of the folio
> > being locked? I don't think so...
> >
> > - Ahh, perhaps its as simple as your fix has removed the code that removed the
> > folio from the deferred split queue if it fails to get a reference? That could
> > mean we end up returning 0 instead of SHRINK_STOP too. I'll have play.
> >
>
> I tested the last idea by adding this back in:
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index d46897d7ea7f..50b07362923a 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3327,8 +3327,12 @@ static unsigned long deferred_split_scan(struct shrinker
> *shrink,
> /* Take ref on all folios to avoid freeing them under us */
> list_for_each_entry_safe(folio, next, &ds_queue->split_queue,
> _deferred_list) {
> - if (!folio_try_get(folio))
> + if (!folio_try_get(folio)) {
> + /* We lost race with folio_put() */
> + list_del_init(&folio->_deferred_list);
> + ds_queue->split_queue_len--;
> continue;
> + }
> if (folio_batch_add(&batch, folio) == 0) {
> --sc->nr_to_scan;
> break;
>
> The test now gets further than where it was previously getting live-locked, but
If the deferred_split_lock contention comes back, we can fix
split_huge_page_to_list() to only take the lock if the page is on the
list. Right now, it takes it unconditionally which could be avoided.
I'm not going to send a patch just yet to avoid confusion.
next prev parent reply other threads:[~2024-03-08 15:33 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-27 17:42 [PATCH v3 00/18] Rearrange batched folio freeing Matthew Wilcox (Oracle)
2024-02-27 17:42 ` [PATCH v3 01/18] mm: Make folios_put() the basis of release_pages() Matthew Wilcox (Oracle)
2024-02-27 17:42 ` [PATCH v3 02/18] mm: Convert free_unref_page_list() to use folios Matthew Wilcox (Oracle)
2024-02-27 17:42 ` [PATCH v3 03/18] mm: Add free_unref_folios() Matthew Wilcox (Oracle)
2024-02-27 17:42 ` [PATCH v3 04/18] mm: Use folios_put() in __folio_batch_release() Matthew Wilcox (Oracle)
2024-02-27 17:42 ` [PATCH v3 05/18] memcg: Add mem_cgroup_uncharge_folios() Matthew Wilcox (Oracle)
2024-02-27 17:42 ` [PATCH v3 06/18] mm: Remove use of folio list from folios_put() Matthew Wilcox (Oracle)
2024-02-27 17:42 ` [PATCH v3 07/18] mm: Use free_unref_folios() in put_pages_list() Matthew Wilcox (Oracle)
2024-02-27 17:42 ` [PATCH v3 08/18] mm: use __page_cache_release() in folios_put() Matthew Wilcox (Oracle)
2024-02-27 17:42 ` [PATCH v3 09/18] mm: Handle large folios in free_unref_folios() Matthew Wilcox (Oracle)
2024-02-27 17:42 ` [PATCH v3 10/18] mm: Allow non-hugetlb large folios to be batch processed Matthew Wilcox (Oracle)
2024-03-06 13:42 ` Ryan Roberts
2024-03-06 16:09 ` Matthew Wilcox
2024-03-06 16:19 ` Ryan Roberts
2024-03-06 17:41 ` Ryan Roberts
2024-03-06 18:41 ` Zi Yan
2024-03-06 19:55 ` Matthew Wilcox
2024-03-06 21:55 ` Matthew Wilcox
2024-03-07 8:56 ` Ryan Roberts
2024-03-07 13:50 ` Yin, Fengwei
2024-03-07 14:05 ` Re: Matthew Wilcox
2024-03-07 15:24 ` Re: Ryan Roberts
2024-03-07 16:24 ` Re: Ryan Roberts
2024-03-07 23:02 ` Re: Matthew Wilcox
2024-03-08 1:06 ` Re: Yin, Fengwei
2024-03-07 17:33 ` [PATCH v3 10/18] mm: Allow non-hugetlb large folios to be batch processed Matthew Wilcox
2024-03-07 18:35 ` Ryan Roberts
2024-03-07 20:42 ` Matthew Wilcox
2024-03-08 11:44 ` Ryan Roberts
2024-03-08 12:09 ` Ryan Roberts
2024-03-08 14:21 ` Ryan Roberts
2024-03-08 15:11 ` Matthew Wilcox
2024-03-08 16:03 ` Matthew Wilcox
2024-03-08 17:13 ` Ryan Roberts
2024-03-08 18:09 ` Ryan Roberts
2024-03-08 18:18 ` Matthew Wilcox
2024-03-09 4:34 ` Andrew Morton
2024-03-09 4:52 ` Matthew Wilcox
2024-03-09 8:05 ` Ryan Roberts
2024-03-09 12:33 ` Ryan Roberts
2024-03-10 13:38 ` Matthew Wilcox
2024-03-08 15:33 ` Matthew Wilcox [this message]
2024-03-09 6:09 ` Matthew Wilcox
2024-03-09 7:59 ` Ryan Roberts
2024-03-09 8:18 ` Ryan Roberts
2024-03-09 9:38 ` Ryan Roberts
2024-03-10 4:23 ` Matthew Wilcox
2024-03-10 8:23 ` Ryan Roberts
2024-03-10 11:08 ` Matthew Wilcox
2024-03-10 11:01 ` Ryan Roberts
2024-03-10 11:11 ` Matthew Wilcox
2024-03-10 16:31 ` Ryan Roberts
2024-03-10 19:57 ` Matthew Wilcox
2024-03-10 19:59 ` Ryan Roberts
2024-03-10 20:46 ` Matthew Wilcox
2024-03-10 21:52 ` Matthew Wilcox
2024-03-11 9:01 ` Ryan Roberts
2024-03-11 12:26 ` Matthew Wilcox
2024-03-11 12:36 ` Ryan Roberts
2024-03-11 15:50 ` Matthew Wilcox
2024-03-11 16:14 ` Ryan Roberts
2024-03-11 17:49 ` Matthew Wilcox
2024-03-12 11:57 ` Ryan Roberts
2024-03-11 19:26 ` Matthew Wilcox
2024-03-10 11:14 ` Ryan Roberts
2024-02-27 17:42 ` [PATCH v3 11/18] mm: Free folios in a batch in shrink_folio_list() Matthew Wilcox (Oracle)
2024-02-27 17:42 ` [PATCH v3 12/18] mm: Free folios directly in move_folios_to_lru() Matthew Wilcox (Oracle)
2024-02-27 17:42 ` [PATCH v3 13/18] memcg: Remove mem_cgroup_uncharge_list() Matthew Wilcox (Oracle)
2024-02-27 17:42 ` [PATCH v3 14/18] mm: Remove free_unref_page_list() Matthew Wilcox (Oracle)
2024-02-27 17:42 ` [PATCH v3 15/18] mm: Remove lru_to_page() Matthew Wilcox (Oracle)
2024-02-27 17:42 ` [PATCH v3 16/18] mm: Convert free_pages_and_swap_cache() to use folios_put() Matthew Wilcox (Oracle)
2024-02-27 17:42 ` [PATCH v3 17/18] mm: Use a folio in __collapse_huge_page_copy_succeeded() Matthew Wilcox (Oracle)
2024-02-27 17:42 ` [PATCH v3 18/18] mm: Convert free_swap_cache() to take a folio Matthew Wilcox (Oracle)
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