Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935229AbcCJJyT (ORCPT ); Thu, 10 Mar 2016 04:54:19 -0500 Received: from mail-wm0-f45.google.com ([74.125.82.45]:34463 "EHLO mail-wm0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754684AbcCJJyB (ORCPT ); Thu, 10 Mar 2016 04:54:01 -0500 Date: Thu, 10 Mar 2016 12:53:58 +0300 From: "Kirill A. Shutemov" To: Ebru Akagunduz Cc: linux-mm@kvack.org, hughd@google.com, riel@redhat.com, akpm@linux-foundation.org, kirill.shutemov@linux.intel.com, n-horiguchi@ah.jp.nec.com, aarcange@redhat.com, iamjoonsoo.kim@lge.com, gorcunov@openvz.org, linux-kernel@vger.kernel.org, mgorman@suse.de, rientjes@google.com, vbabka@suse.cz, aneesh.kumar@linux.vnet.ibm.com, hannes@cmpxchg.org, mhocko@suse.cz, boaz@plexistor.com Subject: Re: [PATCH] mm: avoid unnecessary swapin in khugepaged Message-ID: <20160310095358.GA25372@node.shutemov.name> References: <1457560543-15910-1-git-send-email-ebru.akagunduz@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1457560543-15910-1-git-send-email-ebru.akagunduz@gmail.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3391 Lines: 82 On Wed, Mar 09, 2016 at 11:55:43PM +0200, Ebru Akagunduz wrote: > Currently khugepaged makes swapin readahead to improve > THP collapse rate. This patch checks vm statistics > to avoid workload of swapin, if unnecessary. So that > when system under pressure, khugepaged won't consume > resources to swapin. > > The patch was tested with a test program that allocates > 800MB of memory, writes to it, and then sleeps. The system > was forced to swap out all. Afterwards, the test program > touches the area by writing, it skips a page in each > 20 pages of the area. When waiting to swapin readahead > left part of the test, the memory forced to be busy > doing page reclaim. There was enough free memory during > test, khugepaged did not swapin readahead due to business. > > Test results: > > After swapped out > ------------------------------------------------------------------- > | Anonymous | AnonHugePages | Swap | Fraction | > ------------------------------------------------------------------- > With patch | 450964 kB | 450560 kB | 349036 kB | %99 | > ------------------------------------------------------------------- > Without patch | 351308 kB | 350208 kB | 448692 kB | %99 | > ------------------------------------------------------------------- > > After swapped in (waiting 10 minutes) > ------------------------------------------------------------------- > | Anonymous | AnonHugePages | Swap | Fraction | > ------------------------------------------------------------------- > With patch | 637932 kB | 559104 kB | 162068 kB | %69 | > ------------------------------------------------------------------- > Without patch | 586816 kB | 464896 kB | 213184 kB | %79 | > ------------------------------------------------------------------- > > Signed-off-by: Ebru Akagunduz > --- > mm/huge_memory.c | 15 ++++++++++++++- > 1 file changed, 14 insertions(+), 1 deletion(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 7f75292..109a2af 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -102,6 +102,7 @@ static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait); > */ > static unsigned int khugepaged_max_ptes_none __read_mostly; > static unsigned int khugepaged_max_ptes_swap __read_mostly; > +static unsigned long int allocstall = 0; > > static int khugepaged(void *none); > static int khugepaged_slab_init(void); > @@ -2411,6 +2412,7 @@ static void collapse_huge_page(struct mm_struct *mm, > struct mem_cgroup *memcg; > unsigned long mmun_start; /* For mmu_notifiers */ > unsigned long mmun_end; /* For mmu_notifiers */ > + unsigned long events[NR_VM_EVENT_ITEMS], swap = 0; collapse_huge_page() is nested under collapse_huge_page(), so you effectively allocate 2 * NR_VM_EVENT_ITEMS * sizeof(long) on stack. That's a lot for stack. And it's only get total value of ALLOCSTALL event. Should we instead introduce a helper to sum values of a particular event over all cpu? I'm surprised that we don't have any yet. Something like this (totally untested): unsigned long sum_vm_event(enum vm_event_item item) { int cpu; unsigned long ret = 0; get_online_cpus(); for_each_online_cpu(cpu) ret += per_cpu(vm_event_states, cpu).event[item]; put_online_cpus(); return ret; } -- Kirill A. Shutemov