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

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Message-ID: <20200917214059.GA162800@xz-x1>
Date:   Thu, 17 Sep 2020 17:40:59 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     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 Thu, Sep 17, 2020 at 01:35:56PM -0700, Linus Torvalds wrote:
> For that to happen, we'd need to have the vma flag so that we wouldn't
> have any worry about non-pinners, but as you suggested, I think even
> just a mm-wide counter - or flag - to deal with the fast-bup case is
> likely perfectly sufficient.

Would mm_struct.pinned_vm suffice?

Though now I'm not 100% certain whether all pin_user_pages*() callers are
accounting correctly upon pinned_vm.  My gut feeling is that bc3e53f682d93df67
does not convert all the old locked_vm users with page pinnings (e.g.,
mm_iommu_do_alloc, vaddr_get_pfn, etc.; didn't try harder).

-- 
Peter Xu