linux-kernel - Re: [PATCH] mm/page_alloc: add one PCP list for THP

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Date: Thu, 20 Jun 2024 09:07:46 +0800
From: Ge Yang <yangge1116@....com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, stable@...r.kernel.org,
 21cnbao@...il.com, baolin.wang@...ux.alibaba.com,
 mgorman@...hsingularity.net, liuzixing@...on.cn
Subject: Re: [PATCH] mm/page_alloc: add one PCP list for THP



在 2024/6/20 9:01, Andrew Morton 写道:
> On Wed, 19 Jun 2024 20:54:32 +0800 yangge1116@....com wrote:
> 
>> From: yangge <yangge1116@....com>
>>
>> Since commit 5d0a661d808f ("mm/page_alloc: use only one PCP list for
>> THP-sized allocations") no longer differentiates the migration type
>> of pages in THP-sized PCP list, it's possible that non-movable
>> allocation requests may get a CMA page from the list, in some cases,
>> it's not acceptable.
>>
>> If a large number of CMA memory are configured in system (for
>> example, the CMA memory accounts for 50% of the system memory),
>> starting a virtual machine with device passthrough will get stuck.
>> During starting the virtual machine, it will call
>> pin_user_pages_remote(..., FOLL_LONGTERM, ...) to pin memory. Normally
>> if a page is present and in CMA area, pin_user_pages_remote() will
>> migrate the page from CMA area to non-CMA area because of
>> FOLL_LONGTERM flag. But if non-movable allocation requests return
>> CMA memory, migrate_longterm_unpinnable_pages() will migrate a CMA
>> page to another CMA page, which will fail to pass the check in
>> check_and_migrate_movable_pages() and cause migration endless.
>> Call trace:
> 
> Thanks.  I'll add this for testing - please send us a new version which
> addresses Barry's comments.

Ok, thanks.
New version: 
https://lore.kernel.org/lkml/1718845190-4456-1-git-send-email-yangge1116@126.com/