linux-kernel - Re: [PATCH 01/18] mm: Make mmap_sem for write waits killable for mm syscalls

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Date:	Thu, 10 Mar 2016 16:56:55 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	Alex Deucher <alexander.deucher@....com>,
	Alex Thorlton <athorlton@....com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Christian König <christian.koenig@....com>,
	Daniel Vetter <daniel.vetter@...el.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	David Airlie <airlied@...ux.ie>,
	Davidlohr Bueso <dave@...olabs.net>,
	David Rientjes <rientjes@...gle.com>,
	"H . Peter Anvin" <hpa@...or.com>, Hugh Dickins <hughd@...gle.com>,
	Ingo Molnar <mingo@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	linux-arch@...r.kernel.org, Mel Gorman <mgorman@...e.de>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Petr Cermak <petrcermak@...omium.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 01/18] mm: Make mmap_sem for write waits killable for mm
 syscalls

On Thu 10-03-16 16:47:16, Vlastimil Babka wrote:
> On 02/29/2016 02:26 PM, Michal Hocko wrote:
> >From: Michal Hocko <mhocko@...e.com>
> >
> >This is the first step in making mmap_sem write holders killable. It
> 
> s/holders/waiters/?

right. Fixed
 
> >focuses on the trivial ones which are taking the lock early after
> >entering the syscall and they are not changing state before.
> >
> >Therefore it is very easy to change them to use down_write_killable
> >and immediately return with -EINTR. This will allow the waiter to
> >pass away without blocking the mmap_sem which might be required to
> >make a forward progress. E.g. the oom reaper will need the lock for
> >reading to dismantle the OOM victim address space.
> >
> >The only tricky function in this patch is vm_mmap_pgoff which has many
> >call sites via vm_mmap. To reduce the risk keep vm_mmap with the
> >original non-killable semantic for now.
> >
> >vm_munmap callers do not bother checking the return value so open code
> >it into the munmap syscall path for now for simplicity.
> >
> >Cc: Mel Gorman <mgorman@...e.de>
> >Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> >Cc: Konstantin Khlebnikov <koct9i@...il.com>
> >Cc: Hugh Dickins <hughd@...gle.com>
> >Cc: Andrea Arcangeli <aarcange@...hat.com>
> >Cc: David Rientjes <rientjes@...gle.com>
> >Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> >Cc: Johannes Weiner <hannes@...xchg.org>
> >Signed-off-by: Michal Hocko <mhocko@...e.com>
> 
> Acked-by: Vlastimil Babka <vbabka@...e.cz>

Thanks!
-- 
Michal Hocko
SUSE Labs