Re: [PATCH v5 1/2] btrfs: always uses root memcgroup for filemap_add_folio()

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

在 2024/7/19 16:38, Michal Hocko 写道:
> On Fri 19-07-24 14:19:05, Qu Wenruo wrote:
> [...]
>> @@ -2981,8 +2982,17 @@ static int attach_eb_folio_to_filemap(struct extent_buffer *eb, int i,
>>   	ASSERT(eb->folios[i]);
>>
>>   retry:
>> +	/*
>> +	 * Btree inode is a btrfs internal inode, and not exposed to any
>> +	 * user.
>> +	 * Furthermore we do not want any cgroup limits on this inode.
>> +	 * So we always use root_mem_cgroup as our active memcg when attaching
>> +	 * the folios.
>> +	 */
>> +	old_memcg = set_active_memcg(root_mem_cgroup);
>>   	ret = filemap_add_folio(mapping, eb->folios[i], index + i,
>>   				GFP_NOFS | __GFP_NOFAIL);
>> +	set_active_memcg(old_memcg);
>
> I do not think this will compile with CONFIG_MEMCG=n

My bad.

I'll fix it from the btrfs part so that @root_mem_cgroup would be
changed to NULL for the CONFIG_MEMCG=n case.

Meanwhile, can we just define root_mem_cgroup as NULL globally?
That looks more reasonable to me, and if that's fine I can send out an
extra patch just for that.

Thanks,
Qu

>
>>   	if (!ret)
>>   		goto finish;
>>
>> --
>> 2.45.2
>