linux-kernel - Re: [PATCH v4] mm: Add MREMAP

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Message-ID: <20200213120813.myanzyjmpyzixghf@box>
Date:   Thu, 13 Feb 2020 15:08:13 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Brian Geffon <bgeffon@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, linux-api@...r.kernel.org,
        Andy Lutomirski <luto@...capital.net>,
        Will Deacon <will@...nel.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Sonny Rao <sonnyrao@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Yu Zhao <yuzhao@...gle.com>,
        Jesse Barnes <jsbarnes@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Florian Weimer <fweimer@...hat.com>
Subject: Re: [PATCH v4] mm: Add MREMAP_DONTUNMAP to mremap().

On Mon, Feb 10, 2020 at 06:12:39AM -0800, Brian Geffon wrote:
> Hi Kirill,
> If the old_len == new_len then there is no change in the number of
> locked pages they just moved, if the new_len < old_len then the
> process of unmapping (new_len - old_len) bytes from the old mapping
> will handle the locked page accounting. So in this special case where
> we're growing the VMA, vma_to_resize() will enforce that growing the
> vma doesn't exceed RLIMIT_MEMLOCK, but vma_to_resize() doesn't handle
> incrementing mm->locked_bytes which is why we have that special case
> incrementing it here.

But if you do the operation for the VM_LOCKED vma, you'll have two locked
VMA's now, right? Where do you account the old locked vma you left behind?

-- 
 Kirill A. Shutemov