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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Davidlohr Bueso <davidlohr@hp.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Ingo Molnar <mingo@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Michel Lespinasse <walken@google.com>,
	Mel Gorman <mgorman@suse.de>, Rik van Riel <riel@redhat.com>,
	KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
	"Chandramouleeswaran, Aswin" <aswin@hp.com>,
	"Norton, Scott J" <scott.norton@hp.com>,
	linux-mm <linux-mm@kvack.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] mm: per-thread vma caching
Date: Tue, 25 Feb 2014 10:45:51 -0800	[thread overview]
Message-ID: <CA+55aFxdUOALfQketaSAA9B_Da+n=hSvC5XswV+5cpmnyLwiFw@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFzPYZnkSQa=Y4Uo3zMVUVdchVxN2S266KyZLu-yJ314pw@mail.gmail.com>

On Tue, Feb 25, 2014 at 10:37 AM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
>  - clear all the cache entries (of the new 'struct task_struct'! - so
> not in dup_mmap, but make sure it's zeroed when allocating!)(
>
>  - set vmcache_seqnum to 0 in dup_mmap (since any sequence number is
> fine when it got invalidated, and 0 is best for "avoid overflow").

Btw, as far as I can tell, that also makes the per-thread vmacache
automatically do the right thing for the non-MMU case, so that you
could just remove the difference between CONFIG_MMU and NOMMU.

Basically, dup_mmap() should no longer have anything to do with the
vmacache, since it is now per-thread, not per-mm.

So :

 - allocating a new "struct mm_struct" should clear the
vmacache_seqnum for that new mm, to try to minimize unnecessary future
overflow.

 - thread allocation should just zero the cache entries, and set
"tsk->vmacache_seqnum = mm->vmacache_seqnum" (after dup_mm()) to avoid
future unnecessary flushes.

and as far as I can tell, the logic would be exactly the same on NOMMU
(the dup_mm just doesn't happen, since all forks are basically sharing
mm).

And maybe you'd want to make VMACACHE_SIZE be 1 on NOMMU (and make
sure to change the "& 3" to "& (VMACACHE_SIZE-1)". Just to keep the
size down on small systems that really don't need it.

          Linus

WARNING: multiple messages have this Message-ID (diff)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Davidlohr Bueso <davidlohr@hp.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Ingo Molnar <mingo@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Michel Lespinasse <walken@google.com>,
	Mel Gorman <mgorman@suse.de>, Rik van Riel <riel@redhat.com>,
	KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
	"Chandramouleeswaran, Aswin" <aswin@hp.com>,
	"Norton, Scott J" <scott.norton@hp.com>,
	linux-mm <linux-mm@kvack.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] mm: per-thread vma caching
Date: Tue, 25 Feb 2014 10:45:51 -0800	[thread overview]
Message-ID: <CA+55aFxdUOALfQketaSAA9B_Da+n=hSvC5XswV+5cpmnyLwiFw@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFzPYZnkSQa=Y4Uo3zMVUVdchVxN2S266KyZLu-yJ314pw@mail.gmail.com>

On Tue, Feb 25, 2014 at 10:37 AM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
>  - clear all the cache entries (of the new 'struct task_struct'! - so
> not in dup_mmap, but make sure it's zeroed when allocating!)(
>
>  - set vmcache_seqnum to 0 in dup_mmap (since any sequence number is
> fine when it got invalidated, and 0 is best for "avoid overflow").

Btw, as far as I can tell, that also makes the per-thread vmacache
automatically do the right thing for the non-MMU case, so that you
could just remove the difference between CONFIG_MMU and NOMMU.

Basically, dup_mmap() should no longer have anything to do with the
vmacache, since it is now per-thread, not per-mm.

So :

 - allocating a new "struct mm_struct" should clear the
vmacache_seqnum for that new mm, to try to minimize unnecessary future
overflow.

 - thread allocation should just zero the cache entries, and set
"tsk->vmacache_seqnum = mm->vmacache_seqnum" (after dup_mm()) to avoid
future unnecessary flushes.

and as far as I can tell, the logic would be exactly the same on NOMMU
(the dup_mm just doesn't happen, since all forks are basically sharing
mm).

And maybe you'd want to make VMACACHE_SIZE be 1 on NOMMU (and make
sure to change the "& 3" to "& (VMACACHE_SIZE-1)". Just to keep the
size down on small systems that really don't need it.

          Linus

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  reply	other threads:[~2014-02-25 18:45 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-02-25 18:16 [PATCH v2] mm: per-thread vma caching Davidlohr Bueso
2014-02-25 18:16 ` Davidlohr Bueso
2014-02-25 18:24 ` Rik van Riel
2014-02-25 18:24   ` Rik van Riel
2014-02-25 18:36   ` Davidlohr Bueso
2014-02-25 18:36     ` Davidlohr Bueso
2014-02-25 18:35 ` Peter Zijlstra
2014-02-25 18:35   ` Peter Zijlstra
2014-02-25 18:37   ` Davidlohr Bueso
2014-02-25 18:37     ` Davidlohr Bueso
2014-02-25 19:46     ` Peter Zijlstra
2014-02-25 19:46       ` Peter Zijlstra
2014-02-25 18:37 ` Linus Torvalds
2014-02-25 18:37   ` Linus Torvalds
2014-02-25 18:45   ` Linus Torvalds [this message]
2014-02-25 18:45     ` Linus Torvalds
2014-02-25 19:04   ` Davidlohr Bueso
2014-02-25 19:04     ` Davidlohr Bueso
2014-02-25 19:30     ` Davidlohr Bueso
2014-02-25 19:30       ` Davidlohr Bueso
2014-02-25 19:31     ` Linus Torvalds
2014-02-25 19:31       ` Linus Torvalds
2014-02-26  2:04 ` Michel Lespinasse
2014-02-26  2:04   ` Michel Lespinasse
2014-02-26  4:04   ` Davidlohr Bueso
2014-02-26  4:04     ` Davidlohr Bueso
2014-02-26  7:52     ` Michel Lespinasse
2014-02-26  7:52       ` Michel Lespinasse
2014-02-26  8:50 ` Peter Zijlstra
2014-02-26  8:50   ` Peter Zijlstra
2014-02-26  8:55   ` Peter Zijlstra
2014-02-26  8:55     ` Peter Zijlstra
2014-02-26 11:26 ` Mel Gorman
2014-02-26 11:26   ` Mel Gorman
2014-02-26 19:11   ` Davidlohr Bueso
2014-02-26 19:11     ` Davidlohr Bueso

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