linux-kernel - Re: [PATCH] mm/list_lru: Optimize memcg_drain_list_lru

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Date:   Tue, 8 Mar 2022 20:06:45 -0500
From:   Waiman Long <longman@...hat.com>
To:     Roman Gushchin <roman.gushchin@...ux.dev>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>
Subject: Re: [PATCH] mm/list_lru: Optimize memcg_drain_list_lru_node()

On 3/8/22 19:50, Waiman Long wrote:
> On 3/8/22 19:17, Roman Gushchin wrote:
>> On Tue, Mar 08, 2022 at 10:41:38AM -0500, Waiman Long wrote:
>>> On 3/7/22 23:39, Roman Gushchin wrote:
>>>> On Mon, Mar 07, 2022 at 10:30:09PM -0500, Waiman Long wrote:
>>>>> Since commit 2c80cd57c743 ("mm/list_lru.c: fix list_lru_count_node()
>>>>> to be race free"), we are tracking the total number of lru
>>>>> entries in a list_lru_node in its nr_items field.  In the case of
>>>>> memcg_drain_list_lru_node(), there is nothing to be done if nr_items
>>>>> is 0.  We don't even need to take the nlru->lock as no new lru entry
>>>>> could be added by a racing list_lru_add() to the draining src_idx 
>>>>> memcg
>>>>> at this point.
>>>>>
>>>>> Signed-off-by: Waiman Long <longman@...hat.com>
>>>> Hi Waiman!
>>>>
>>>> The patch makes total sense to me, however it needs to be rebased 
>>>> at least
>>>> on top of "mm: list_lru: rename memcg_drain_all_list_lrus to 
>>>> memcg_reparent_list_lrus".
>>>>
>>>> Thanks!
>>>>
>>>>
>>> This patch was based on the current linux-next tree which includes 
>>> commit
>>> ff221bc26bdd ("mm: list_lru: rename memcg_drain_all_list_lrus to
>>> memcg_reparent_list_lrus"). I do remember to double-check linux-next 
>>> before
>>> sending this patch out. In fact, the same patch can be applied to 
>>> both linux
>>> and linux-next tree without problem.
>> I'm looking at the mm tree (https://github.com/hnaz/linux-mm.git) and 
>> clearly
>> see that commit "mm: list_lru: rename memcg_drain_all_list_lrus to
>> memcg_reparent_list_lrus" eliminated the function with the name
>> memcg_drain_list_lru_node(), which your patch is touching.
>> Currently the function is located in list_lru.c and is named
>> memcg_reparent_list_lru_node().
>>
>> linux-next is sometimes a bit behind the mm tree.
>
> Oh, you are right. I will rebase the patch based on linux-mm.
>
> Thanks for the suggestion.

The patch was originally based on the linux tree. Then I applied it onto 
linux-next without any issue. Unfortunately, I failed to notice that the 
hunk was applied to memcg_reparent_list_lru_node() without realizing 
that it is the new name for the old memcg_drain_list_lru_node(). The 
linux-next tree that I used does have all the necessary patches.

Cheers,
Longman