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From: David Hildenbrand <david@redhat.com>
To: Minchan Kim <minchan@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	joaodias@google.com, surenb@google.com, cgoldswo@codeaurora.org,
	willy@infradead.org, mhocko@suse.com, vbabka@suse.cz,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v3 2/3] mm: disable LRU pagevec during the migration temporarily
Date: Fri, 12 Mar 2021 10:00:28 +0100	[thread overview]
Message-ID: <5ada6223-ce21-1ae4-8580-5cd25ed491b5@redhat.com> (raw)
In-Reply-To: <20210310161429.399432-2-minchan@kernel.org>

On 10.03.21 17:14, Minchan Kim wrote:
> LRU pagevec holds refcount of pages until the pagevec are drained.
> It could prevent migration since the refcount of the page is greater
> than the expection in migration logic. To mitigate the issue,
> callers of migrate_pages drains LRU pagevec via migrate_prep or
> lru_add_drain_all before migrate_pages call.
> 
> However, it's not enough because pages coming into pagevec after the
> draining call still could stay at the pagevec so it could keep
> preventing page migration. Since some callers of migrate_pages have
> retrial logic with LRU draining, the page would migrate at next trail
> but it is still fragile in that it doesn't close the fundamental race
> between upcoming LRU pages into pagvec and migration so the migration
> failure could cause contiguous memory allocation failure in the end.
> 
> To close the race, this patch disables lru caches(i.e, pagevec)
> during ongoing migration until migrate is done.
> 
> Since it's really hard to reproduce, I measured how many times
> migrate_pages retried with force mode(it is about a fallback to a
> sync migration) with below debug code.
> 
> int migrate_pages(struct list_head *from, new_page_t get_new_page,
> 			..
> 			..
> 
> if (rc && reason == MR_CONTIG_RANGE && pass > 2) {
>         printk(KERN_ERR, "pfn 0x%lx reason %d\n", page_to_pfn(page), rc);
>         dump_page(page, "fail to migrate");
> }
> 
> The test was repeating android apps launching with cma allocation
> in background every five seconds. Total cma allocation count was
> about 500 during the testing. With this patch, the dump_page count
> was reduced from 400 to 30.
> 
> The new interface is also useful for memory hotplug which currently
> drains lru pcp caches after each migration failure. This is rather
> suboptimal as it has to disrupt others running during the operation.
> With the new interface the operation happens only once. This is also in
> line with pcp allocator cache which are disabled for the offlining as
> well.
> 
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
>   include/linux/swap.h |  3 ++
>   mm/memory_hotplug.c  |  3 +-
>   mm/mempolicy.c       |  4 ++-
>   mm/migrate.c         |  3 +-
>   mm/swap.c            | 79 ++++++++++++++++++++++++++++++++++++--------
>   5 files changed, 75 insertions(+), 17 deletions(-)
> 
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 32f665b1ee85..a3e258335a7f 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -339,6 +339,9 @@ extern void lru_note_cost(struct lruvec *lruvec, bool file,
>   extern void lru_note_cost_page(struct page *);
>   extern void lru_cache_add(struct page *);
>   extern void mark_page_accessed(struct page *);
> +extern void lru_cache_disable(void);
> +extern void lru_cache_enable(void);
> +extern bool lru_cache_disabled(void);
>   extern void lru_add_drain(void);
>   extern void lru_add_drain_cpu(int cpu);
>   extern void lru_add_drain_cpu_zone(struct zone *zone);
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 5ba51a8bdaeb..959f659ef085 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1611,6 +1611,7 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
>   	 * in a way that pages from isolated pageblock are left on pcplists.
>   	 */
>   	zone_pcp_disable(zone);
> +	lru_cache_disable();

Did you also experiment which effects zone_pcp_disable() might have on 
alloc_contig_range() ?

Feels like both calls could be abstracted somehow and used in both 
(memory offlining/alloc_contig_range) cases. It's essentially disabling 
some kind of caching.


Looks sane to me, but I am not that experienced with migration code to 
give this a real RB.

-- 
Thanks,

David / dhildenb


  parent reply	other threads:[~2021-03-12  9:01 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-10 16:14 [PATCH v3 1/3] mm: replace migrate_prep with lru_add_drain_all Minchan Kim
2021-03-10 16:14 ` [PATCH v3 2/3] mm: disable LRU pagevec during the migration temporarily Minchan Kim
2021-03-11 22:41   ` Chris Goldsworthy
2021-03-14  5:10     ` Chris Goldsworthy
2021-03-12  8:21   ` Michal Hocko
2021-03-12  9:00   ` David Hildenbrand [this message]
2021-03-18  0:13   ` Andrew Morton
2021-03-18  1:13     ` Minchan Kim
2021-03-18  8:09     ` Michal Hocko
2021-03-10 16:14 ` [PATCH v3 3/3] mm: fs: Invalidate BH LRU during page migration Minchan Kim
2021-03-12  9:03   ` David Hildenbrand
2021-03-12  9:33     ` David Hildenbrand
2021-03-12 17:17       ` Minchan Kim
2021-03-16 18:26         ` Minchan Kim
2021-03-17 11:18           ` David Hildenbrand
2021-03-17  2:37   ` [mm] 8fd8d23ab1: WARNING:at_fs/buffer.c:#__brelse kernel test robot
2021-03-17 16:29     ` Minchan Kim
2021-03-19 14:05       ` Oliver Sang
2021-03-19 16:47         ` Minchan Kim
2021-03-12  8:19 ` [PATCH v3 1/3] mm: replace migrate_prep with lru_add_drain_all Michal Hocko
2021-03-12  8:53 ` David Hildenbrand

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