From: Andrea Arcangeli <aarcange@redhat.com>
To: David Rientjes <rientjes@google.com>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Michael J Wolf <mjwolf@us.ibm.com>
Subject: Re: [RFC][PATCH 1/6] count transparent hugepage splits
Date: Fri, 4 Feb 2011 22:18:25 +0100 [thread overview]
Message-ID: <20110204211825.GJ30909@random.random> (raw)
In-Reply-To: <alpine.DEB.2.00.1102031235100.453@chino.kir.corp.google.com>
On Thu, Feb 03, 2011 at 01:22:14PM -0800, David Rientjes wrote:
> i.e. no global locking, but we've accepted the occassional off-by-one
> error (even though splitting of hugepages isn't by any means lightning
> fast and the overhead of atomic ops would be negligible).
Agreed losing an increment is not a problem, but in very large systems
it will become a bottleneck. It's not super urgent, but I think it
needs to become a per-cpu counter sooner than later (not needed
immediately but I would appreciate an incremental patch soon to
address that). split_huge_page is already fully SMP scalable if the
rmap isn't shared (i.e. fully SMP scalable across different execve)
and I'd like it to stay that way because split_huge_page can run at
high frequency at times from different processes, so in very large
systems it may be measurable, with that cacheline bouncing around 1024
cpus. pages_collapsed is not a problem because it's only used by one
kernel thread so it can't be contended. Again not super urgent but
better to optimize it ;).
WARNING: multiple messages have this Message-ID (diff)
From: Andrea Arcangeli <aarcange@redhat.com>
To: David Rientjes <rientjes@google.com>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Michael J Wolf <mjwolf@us.ibm.com>
Subject: Re: [RFC][PATCH 1/6] count transparent hugepage splits
Date: Fri, 4 Feb 2011 22:18:25 +0100 [thread overview]
Message-ID: <20110204211825.GJ30909@random.random> (raw)
In-Reply-To: <alpine.DEB.2.00.1102031235100.453@chino.kir.corp.google.com>
On Thu, Feb 03, 2011 at 01:22:14PM -0800, David Rientjes wrote:
> i.e. no global locking, but we've accepted the occassional off-by-one
> error (even though splitting of hugepages isn't by any means lightning
> fast and the overhead of atomic ops would be negligible).
Agreed losing an increment is not a problem, but in very large systems
it will become a bottleneck. It's not super urgent, but I think it
needs to become a per-cpu counter sooner than later (not needed
immediately but I would appreciate an incremental patch soon to
address that). split_huge_page is already fully SMP scalable if the
rmap isn't shared (i.e. fully SMP scalable across different execve)
and I'd like it to stay that way because split_huge_page can run at
high frequency at times from different processes, so in very large
systems it may be measurable, with that cacheline bouncing around 1024
cpus. pages_collapsed is not a problem because it's only used by one
kernel thread so it can't be contended. Again not super urgent but
better to optimize it ;).
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next prev parent reply other threads:[~2011-02-04 21:18 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-02-01 0:33 [RFC][PATCH 0/6] more detailed per-process transparent hugepage statistics Dave Hansen
2011-02-01 0:33 ` Dave Hansen
2011-02-01 0:33 ` [RFC][PATCH 1/6] count transparent hugepage splits Dave Hansen
2011-02-01 0:33 ` Dave Hansen
2011-02-01 9:58 ` Johannes Weiner
2011-02-01 9:58 ` Johannes Weiner
2011-02-03 21:22 ` David Rientjes
2011-02-03 21:22 ` David Rientjes
2011-02-04 21:18 ` Andrea Arcangeli [this message]
2011-02-04 21:18 ` Andrea Arcangeli
2011-02-04 21:28 ` Dave Hansen
2011-02-04 21:28 ` Dave Hansen
2011-02-01 0:33 ` [RFC][PATCH 2/6] pagewalk: only split huge pages when necessary Dave Hansen
2011-02-01 0:33 ` Dave Hansen
2011-02-01 10:04 ` Johannes Weiner
2011-02-01 10:04 ` Johannes Weiner
2011-02-01 15:03 ` Dave Hansen
2011-02-01 15:03 ` Dave Hansen
2011-02-03 21:22 ` David Rientjes
2011-02-03 21:22 ` David Rientjes
2011-02-03 21:33 ` Dave Hansen
2011-02-03 21:33 ` Dave Hansen
2011-02-03 21:46 ` David Rientjes
2011-02-03 21:46 ` David Rientjes
2011-02-04 17:19 ` Dave Hansen
2011-02-04 17:19 ` Dave Hansen
2011-02-04 21:10 ` Andrea Arcangeli
2011-02-04 21:10 ` Andrea Arcangeli
2011-02-01 0:34 ` [RFC][PATCH 3/6] break out smaps_pte_entry() from smaps_pte_range() Dave Hansen
2011-02-01 0:34 ` Dave Hansen
2011-02-01 10:08 ` Johannes Weiner
2011-02-01 10:08 ` Johannes Weiner
2011-02-03 21:22 ` David Rientjes
2011-02-03 21:22 ` David Rientjes
2011-02-03 21:40 ` Dave Hansen
2011-02-03 21:40 ` Dave Hansen
2011-02-01 0:34 ` [RFC][PATCH 4/6] pass pte size argument in to smaps_pte_entry() Dave Hansen
2011-02-01 0:34 ` Dave Hansen
2011-02-01 10:09 ` Johannes Weiner
2011-02-01 10:09 ` Johannes Weiner
2011-02-03 21:22 ` David Rientjes
2011-02-03 21:22 ` David Rientjes
2011-02-01 0:34 ` [RFC][PATCH 5/6] teach smaps_pte_range() about THP pmds Dave Hansen
2011-02-01 0:34 ` Dave Hansen
2011-02-01 10:11 ` Johannes Weiner
2011-02-01 10:11 ` Johannes Weiner
2011-02-01 15:02 ` Dave Hansen
2011-02-01 15:02 ` Dave Hansen
2011-02-01 16:09 ` Andrea Arcangeli
2011-02-01 16:09 ` Andrea Arcangeli
2011-02-03 21:22 ` David Rientjes
2011-02-03 21:22 ` David Rientjes
2011-02-03 21:34 ` Dave Hansen
2011-02-03 21:34 ` Dave Hansen
2011-02-01 0:34 ` [RFC][PATCH 6/6] have smaps show transparent huge pages Dave Hansen
2011-02-01 0:34 ` Dave Hansen
2011-02-01 10:12 ` Johannes Weiner
2011-02-01 10:12 ` Johannes Weiner
2011-02-03 21:22 ` David Rientjes
2011-02-03 21:22 ` David Rientjes
2011-02-01 15:38 ` [RFC][PATCH 0/6] more detailed per-process transparent hugepage statistics Andrea Arcangeli
2011-02-01 15:38 ` Andrea Arcangeli
2011-02-01 17:15 ` Dave Hansen
2011-02-01 17:15 ` Dave Hansen
2011-02-01 20:39 ` Andrea Arcangeli
2011-02-01 20:39 ` Andrea Arcangeli
2011-02-01 20:56 ` Dave Hansen
2011-02-01 20:56 ` Dave Hansen
2011-02-02 0:07 ` Andrea Arcangeli
2011-02-02 0:07 ` Andrea Arcangeli
2011-02-08 17:54 ` Dave Hansen
2011-02-08 17:54 ` Dave Hansen
2011-02-08 18:17 ` Andrea Arcangeli
2011-02-08 18:17 ` Andrea Arcangeli
2011-02-03 21:54 ` David Rientjes
2011-02-03 21:54 ` David Rientjes
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