linux-kernel - Re: [PATCH V3 0/5] Allow user to request memory to be locked on page fault

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

On Tue,  7 Jul 2015 13:03:38 -0400 Eric B Munson <emunson@...mai.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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