linux-kernel - Re: [v2 PATCH -mm] mm: account deferred split THPs into MemAvailable

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aaaf9742-56f7-44b7-c3db-ad078b7b2220@suse.cz>
Date:   Tue, 27 Aug 2019 14:01:56 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Michal Hocko <mhocko@...nel.org>
Cc:     kirill.shutemov@...ux.intel.com,
        Yang Shi <yang.shi@...ux.alibaba.com>, hannes@...xchg.org,
        rientjes@...gle.com, akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [v2 PATCH -mm] mm: account deferred split THPs into MemAvailable

On 8/27/19 1:02 PM, Kirill A. Shutemov wrote:
> On Tue, Aug 27, 2019 at 08:01:39AM +0200, Michal Hocko wrote:
>> On Mon 26-08-19 16:15:38, Kirill A. Shutemov wrote:
>>>
>>> Unmapped completely pages will be freed with current code. Deferred split
>>> only applies to partly mapped THPs: at least on 4k of the THP is still
>>> mapped somewhere.
>>
>> Hmm, I am probably misreading the code but at least current Linus' tree
>> reads page_remove_rmap -> [page_remove_anon_compound_rmap ->\ deferred_split_huge_page even
>> for fully mapped THP.
> 
> Well, you read correctly, but it was not intended. I screwed it up at some
> point.
> 
> See the patch below. It should make it work as intened.
> 
> It's not bug as such, but inefficientcy. We add page to the queue where
> it's not needed.

But that adding to queue doesn't affect whether the page will be freed
immediately if there are no more partial mappings, right? I don't see
deferred_split_huge_page() pinning the page.
So your patch wouldn't make THPs freed immediately in cases where they
haven't been freed before immediately, it just fixes a minor
inefficiency with queue manipulation?