linux-kernel - Re: [PATCH v9 3/3] mm/madvise: introduce process_madvise() syscall: an external memory hinting API

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: <20200921071410.GB12990@dhcp22.suse.cz>
Date:   Mon, 21 Sep 2020 09:14:10 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        linux-mm <linux-mm@...ck.org>, linux-api@...r.kernel.org,
        oleksandr@...hat.com, Suren Baghdasaryan <surenb@...gle.com>,
        Tim Murray <timmurray@...gle.com>,
        Sandeep Patil <sspatil@...gle.com>,
        Sonny Rao <sonnyrao@...gle.com>,
        Brian Geffon <bgeffon@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        John Dias <joaodias@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Jann Horn <jannh@...gle.com>,
        alexander.h.duyck@...ux.intel.com, sj38.park@...il.com,
        David Rientjes <rientjes@...gle.com>,
        Arjun Roy <arjunroy@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Christian Brauner <christian@...uner.io>,
        Daniel Colascione <dancol@...gle.com>,
        Jens Axboe <axboe@...nel.dk>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        SeongJae Park <sjpark@...zon.de>, linux-man@...r.kernel.org
Subject: Re: [PATCH v9 3/3] mm/madvise: introduce process_madvise() syscall:
 an external memory hinting API

On Mon 21-09-20 07:56:33, Christoph Hellwig wrote:
> On Mon, Aug 31, 2020 at 05:06:33PM -0700, Minchan Kim wrote:
> > There is usecase that System Management Software(SMS) want to give a
> > memory hint like MADV_[COLD|PAGEEOUT] to other processes and in the
> > case of Android, it is the ActivityManagerService.
> > 
> > The information required to make the reclaim decision is not known to
> > the app.  Instead, it is known to the centralized userspace
> > daemon(ActivityManagerService), and that daemon must be able to
> > initiate reclaim on its own without any app involvement.
> > 
> > To solve the issue, this patch introduces a new syscall process_madvise(2).
> > It uses pidfd of an external process to give the hint. It also supports
> > vector address range because Android app has thousands of vmas due to
> > zygote so it's totally waste of CPU and power if we should call the
> > syscall one by one for each vma.(With testing 2000-vma syscall vs
> > 1-vector syscall, it showed 15% performance improvement.  I think it
> > would be bigger in real practice because the testing ran very cache
> > friendly environment).
> 
> I'm really not sure this syscall is a good idea.  If you want central
> control you should implement an IPC mechanisms that allows your
> supervisor daemon to tell the application to perform the madvice
> instead of forcing the behavior on it.

Even though I am not entirely happy about the interface [1]. As it seems
I am in minority in my concern I backed off and decided to not block this
work because I do not see the problem with the functionality itself. And
I find it very useful for userspace driven memory management people are
asking for a long time.

This functionality shouldn't be much different from the standard memory
reclaim. It has some limitations (e.g. it can only handle mapped memory)
but allows to pro-actively swap out or reclaim disk based memory based
on a specific knowlege of the workload. Kernel is not able to do the
same.

[1] http://lkml.kernel.org/r/20200117115225.GV19428@dhcp22.suse.cz
-- 
Michal Hocko
SUSE Labs