linux-kernel - Re: [PATCH 1/4] mm: Trial do_wp

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Message-ID: <20200921163112.GF5962@xz-x1>
Date:   Mon, 21 Sep 2020 12:31:12 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Christian Brauner <christian.brauner@...ntu.com>,
        Tejun Heo <tj@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        John Hubbard <jhubbard@...dia.com>,
        Leon Romanovsky <leonro@...dia.com>,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Maya B . Gokhale" <gokhale2@...l.gov>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Marty Mcfadden <mcfadden8@...l.gov>,
        Kirill Shutemov <kirill@...temov.name>,
        Oleg Nesterov <oleg@...hat.com>, Jann Horn <jannh@...gle.com>,
        Jan Kara <jack@...e.cz>, Kirill Tkhai <ktkhai@...tuozzo.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/4] mm: Trial do_wp_page() simplification

On Mon, Sep 21, 2020 at 04:57:38PM +0200, Michal Hocko wrote:
> Switching the order wouldn't make much of a difference right. At least
> not for memcg where all the accounted allocations will still go to
> current's memcg.

I think I'll make it simple to charge the parent directly just like what we do
right now.  I do expect that the charged amount could be quite some when
there're a lot pinned pages on the parent process, however hopefully it's
acceptable as it's still a very rare case, and proper MADV_DONTFORK upon pinned
pages on the parent process will eliminate all these charges too.

I actually already prepared some patches.  It's definitely bigger than expected
due to the complexity that we held page table locks in copy_one_pte() when
trying to break the cow pages.  I don't know whether it would be proper any
more for rc, especially the ending of rcs.  Anyway I'll post them out soon
after I did some basic tests, because I think that's something right to do
irrelevant to when it will be merged.

Thanks,

-- 
Peter Xu