Date: Tue, 7 Jul 2015 14:16:13 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Eric B Munson <emunson@akamai.com>
Cc: Shuah Khan <shuahkh@osg.samsung.com>, Michal Hocko <mhocko@suse.cz>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Vlastimil Babka <vbabka@suse.cz>, linux-alpha@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mips@linux-mips.org,
        linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org,
        linux-mm@kvack.org, linux-arch@vger.kernel.org,
        linux-api@vger.kernel.org
Subject: Re: [PATCH V3 0/5] Allow user to request memory to be locked on
 page fault
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On Tue,  7 Jul 2015 13:03:38 -0400 Eric B Munson <emunson@akamai.com> wrote:

> mlock() allows a user to control page out of program memory, but this
> comes at the cost of faulting in the entire mapping when it is
> allocated.  For large mappings where the entire area is not necessary
> this is not ideal.  Instead of forcing all locked pages to be present
> when they are allocated, this set creates a middle ground.  Pages are
> marked to be placed on the unevictable LRU (locked) when they are first
> used, but they are not faulted in by the mlock call.
> 
> This series introduces a new mlock() system call that takes a flags
> argument along with the start address and size.  This flags argument
> gives the caller the ability to request memory be locked in the
> traditional way, or to be locked after the page is faulted in.  New
> calls are added for munlock() and munlockall() which give the called a
> way to specify which flags are supposed to be cleared.  A new MCL flag
> is added to mirror the lock on fault behavior from mlock() in
> mlockall().  Finally, a flag for mmap() is added that allows a user to
> specify that the covered are should not be paged out, but only after the
> memory has been used the first time.

Thanks for sticking with this.  Adding new syscalls is a bit of a
hassle but I do think we end up with a better interface - the existing
mlock/munlock/mlockall interfaces just aren't appropriate for these
things.

I don't know whether these syscalls should be documented via new
manpages, or if we should instead add them to the existing
mlock/munlock/mlockall manpages.  Michael, could you please advise?

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