Re: [External] Re: [PATCH 0/2] mm/zsmalloc: simplify synchronization between zs_page_migrate() and free_zspage()

[Chengming Zhou <zhouchengming@bytedance.com>]

On 2024/2/28 09:57, Sergey Senozhatsky wrote:
> On (24/02/27 03:02), Chengming Zhou wrote:
>> Hello,
>>
>> free_zspage() has to hold locks of all pages, since zs_page_migrate()
>> path rely on this page lock to protect the race between zs_free() and
>> it, so it can safely get zspage from page->private.
>>
>> But this way is not good and simple enough:
>>
>> 1. Since zs_free() couldn't be sleepable, it can only trylock pages,
>>    or has to kick_deferred_free() to defer that to a work.
>>
>> 2. Even in the worker context, async_free_zspage() can't simply
>>    lock all pages in lock_zspage(), it's still trylock because of
>>    the race between zs_free() and zs_page_migrate(). Please see
>>    the commit 2505a981114d ("zsmalloc: fix races between asynchronous
>>    zspage free and page migration") for details.
>>
>> Actually, all free_zspage() needs is to get zspage from page safely,
>> we can use RCU to achieve it easily. Then free_zspage() don't need to
>> hold locks of all pages, so don't need the deferred free mechanism
>> at all. This patchset implements it and remove all of deferred free
>> related code.
>>
>> Thanks for review and comments!
>>
>> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
> 
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Sorry for this, I thought the problem was fixed after testing with my own
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I will always use linux.dev email in the future to avoid these problems.

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