linux-kernel - Re: [PATCH 2/3] mm/memory_hotplug: fix potential permanent lru cache disable

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Message-ID: <3a124653-31de-5eb6-3812-73c4ea20bbbf@huawei.com>
Date:   Mon, 23 Aug 2021 19:13:12 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Oscar Salvador <osalvador@...e.de>
CC:     <akpm@...ux-foundation.org>, <naoya.horiguchi@....com>,
        <mhocko@...e.com>, <minchan@...nel.org>, <cgoldswo@...eaurora.org>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] mm/memory_hotplug: fix potential permanent lru cache
 disable

On 2021/8/23 17:15, Oscar Salvador wrote:
> On 2021-08-21 11:42, Miaohe Lin wrote:
>> If offline_pages failed after lru_cache_disable(), it forgot to do
>> lru_cache_enable() in error path. So we would have lru cache disabled
>> permanently in this case.
>>
>> Fixes: d479960e44f2 ("mm: disable LRU pagevec during the migration temporarily")
>> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> 
> Reviewed-by: Oscar Salvador <osalvador@...e.de>
> 

Many thanks for your review and reply. :)

> Should this go to stable?
> In case we fail to enable it again, we will bypass the pvec cache anytime we add a new page to the LRU which might lead to severe performance regression?
> 

Agree with you. I think this should go to stable too.

>> ---
>>  mm/memory_hotplug.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index d986d3791986..9fd0be32a281 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -2033,6 +2033,7 @@ int __ref offline_pages(unsigned long start_pfn,
>> unsigned long nr_pages,
>>      undo_isolate_page_range(start_pfn, end_pfn, MIGRATE_MOVABLE);
>>      memory_notify(MEM_CANCEL_OFFLINE, &arg);
>>  failed_removal_pcplists_disabled:
>> +    lru_cache_enable();
>>      zone_pcp_enable(zone);
>>  failed_removal:
>>      pr_debug("memory offlining [mem %#010llx-%#010llx] failed due to %s\n",
>