Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030322AbcCQLHx (ORCPT ); Thu, 17 Mar 2016 07:07:53 -0400 Received: from mx2.suse.de ([195.135.220.15]:46340 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932903AbcCQLHt (ORCPT ); Thu, 17 Mar 2016 07:07:49 -0400 Subject: Re: [PATCH v3 2/2] mm, thp: avoid unnecessary swapin in khugepaged To: Ebru Akagunduz , linux-mm@kvack.org References: <1457991611-6211-1-git-send-email-ebru.akagunduz@gmail.com> <1457991611-6211-3-git-send-email-ebru.akagunduz@gmail.com> Cc: 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, aneesh.kumar@linux.vnet.ibm.com, hannes@cmpxchg.org, mhocko@suse.cz, boaz@plexistor.com From: Vlastimil Babka Message-ID: <56EA9000.1070108@suse.cz> Date: Thu, 17 Mar 2016 12:07:44 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: <1457991611-6211-3-git-send-email-ebru.akagunduz@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4672 Lines: 116 On 03/14/2016 10:40 PM, 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 | 206608 kB | 204800 kB | 593392 kB | %99 | > ------------------------------------------------------------------- > Without patch | 351308 kB | 350208 kB | 448692 kB | %99 | > ------------------------------------------------------------------- > > After swapped in (waiting 10 minutes) > ------------------------------------------------------------------- > | Anonymous | AnonHugePages | Swap | Fraction | > ------------------------------------------------------------------- > With patch | 551992 kB | 368640 kB | 248008 kB | %66 | > ------------------------------------------------------------------- > Without patch | 586816 kB | 464896 kB | 213184 kB | %79 | > ------------------------------------------------------------------- > > Signed-off-by: Ebru Akagunduz Looks like a step in a good direction. Still might be worthwile to also wait for the swapin to complete, and actually collapse immediately, no? > --- > Changes in v2: > - Add reference to specify which patch fixed (Ebru Akagunduz) The reference is again missing in v3. > - Fix commit subject line (Ebru Akagunduz) > > Changes in v3: > - Remove default values of allocstall (Kirill A. Shutemov) > > mm/huge_memory.c | 13 +++++++++++-- > 1 file changed, 11 insertions(+), 2 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 86e9666..67a398c 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; "int" here is unnecessary > > static int khugepaged(void *none); > static int khugepaged_slab_init(void); > @@ -2438,7 +2439,7 @@ static void collapse_huge_page(struct mm_struct *mm, > struct page *new_page; > spinlock_t *pmd_ptl, *pte_ptl; > int isolated = 0, result = 0; > - unsigned long hstart, hend; > + unsigned long hstart, hend, swap, curr_allocstall; > struct mem_cgroup *memcg; > unsigned long mmun_start; /* For mmu_notifiers */ > unsigned long mmun_end; /* For mmu_notifiers */ > @@ -2493,7 +2494,14 @@ static void collapse_huge_page(struct mm_struct *mm, > goto out; > } > > - __collapse_huge_page_swapin(mm, vma, address, pmd); > + swap = get_mm_counter(mm, MM_SWAPENTS); > + curr_allocstall = sum_vm_event(ALLOCSTALL); > + /* > + * When system under pressure, don't swapin readahead. > + * So that avoid unnecessary resource consuming. > + */ > + if (allocstall == curr_allocstall && swap != 0) > + __collapse_huge_page_swapin(mm, vma, address, pmd); > > anon_vma_lock_write(vma->anon_vma); > > @@ -2790,6 +2798,7 @@ skip: > VM_BUG_ON(khugepaged_scan.address < hstart || > khugepaged_scan.address + HPAGE_PMD_SIZE > > hend); > + allocstall = sum_vm_event(ALLOCSTALL); Why here? Rik said in v2: > Khugepaged stores the allocstall value when it goes to sleep, > and checks it before calling (or not) __collapse_huge_page_swapin. But that's not true, this is not "when it goes to sleep". So AFAICS it only observes the allocstalls between starting to scan a single pmd, and trying to collapse the pmd. So the window is quite tiny especially compared to I/O speeds, and this will IMHO catch only really frequent stalls. Placing it really at "when it goes to sleep" sounds better. > ret = khugepaged_scan_pmd(mm, vma, > khugepaged_scan.address, > hpage); >