From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753252AbcFOGku (ORCPT ); Wed, 15 Jun 2016 02:40:50 -0400 Received: from LGEAMRELO13.lge.com ([156.147.23.53]:33413 "EHLO lgeamrelo13.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752641AbcFOGks (ORCPT ); Wed, 15 Jun 2016 02:40:48 -0400 X-Original-SENDERIP: 156.147.1.127 X-Original-MAILFROM: minchan@kernel.org X-Original-SENDERIP: 10.177.223.161 X-Original-MAILFROM: minchan@kernel.org Date: Wed, 15 Jun 2016 15:40:53 +0900 From: Minchan Kim 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: [RFC PATCH 2/3] mm, thp: convert from optimistic to conservative Message-ID: <20160615064053.GH17127@bbox> References: <1465672561-29608-1-git-send-email-ebru.akagunduz@gmail.com> <1465672561-29608-3-git-send-email-ebru.akagunduz@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1465672561-29608-3-git-send-email-ebru.akagunduz@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Sat, Jun 11, 2016 at 10:16:00PM +0300, Ebru Akagunduz wrote: > Currently, khugepaged collapses pages saying only > a referenced page enough to create a THP. > > This patch changes the design from optimistic to conservative. > It gives a default threshold which is half of HPAGE_PMD_NR > for referenced pages, also introduces a new sysfs knob. Strictly speaking, It's not what I suggested. I didn't mean that let's change threshold for deciding whether we should collapse or not(although just *a* reference page seems be too optimistic) and export the knob to the user. In fact, I cannot judge whether it's worth or not because I never have an experience with THP workload in practice although I believe it does make sense. What I suggested is that a swapin operation would be much heavier than a THP cost to collapse populated anon page so it should be more conservative than THP collasping decision, at least. Given that thought, decision point for collasping a THP is *a* reference page now so *half* reference of populated pages for reading swapped-out page is more conservative. > > Signed-off-by: Ebru Akagunduz > --- > include/trace/events/huge_memory.h | 10 ++++---- > mm/khugepaged.c | 50 +++++++++++++++++++++++++++++--------- > 2 files changed, 44 insertions(+), 16 deletions(-) > > diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h > index 830d47d..5f14025 100644 > --- a/include/trace/events/huge_memory.h > +++ b/include/trace/events/huge_memory.h > @@ -13,7 +13,7 @@ > EM( SCAN_EXCEED_NONE_PTE, "exceed_none_pte") \ > EM( SCAN_PTE_NON_PRESENT, "pte_non_present") \ > EM( SCAN_PAGE_RO, "no_writable_page") \ > - EM( SCAN_NO_REFERENCED_PAGE, "no_referenced_page") \ > + EM( SCAN_LACK_REFERENCED_PAGE, "lack_referenced_page") \ > EM( SCAN_PAGE_NULL, "page_null") \ > EM( SCAN_SCAN_ABORT, "scan_aborted") \ > EM( SCAN_PAGE_COUNT, "not_suitable_page_count") \ > @@ -47,7 +47,7 @@ SCAN_STATUS > TRACE_EVENT(mm_khugepaged_scan_pmd, > > TP_PROTO(struct mm_struct *mm, struct page *page, bool writable, > - bool referenced, int none_or_zero, int status, int unmapped), > + int referenced, int none_or_zero, int status, int unmapped), > > TP_ARGS(mm, page, writable, referenced, none_or_zero, status, unmapped), > > @@ -55,7 +55,7 @@ TRACE_EVENT(mm_khugepaged_scan_pmd, > __field(struct mm_struct *, mm) > __field(unsigned long, pfn) > __field(bool, writable) > - __field(bool, referenced) > + __field(int, referenced) > __field(int, none_or_zero) > __field(int, status) > __field(int, unmapped) > @@ -108,14 +108,14 @@ TRACE_EVENT(mm_collapse_huge_page, > TRACE_EVENT(mm_collapse_huge_page_isolate, > > TP_PROTO(struct page *page, int none_or_zero, > - bool referenced, bool writable, int status), > + int referenced, bool writable, int status), > > TP_ARGS(page, none_or_zero, referenced, writable, status), > > TP_STRUCT__entry( > __field(unsigned long, pfn) > __field(int, none_or_zero) > - __field(bool, referenced) > + __field(int, referenced) > __field(bool, writable) > __field(int, status) > ), > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index e3d8da7..43fc41e 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -27,7 +27,7 @@ enum scan_result { > SCAN_EXCEED_NONE_PTE, > SCAN_PTE_NON_PRESENT, > SCAN_PAGE_RO, > - SCAN_NO_REFERENCED_PAGE, > + SCAN_LACK_REFERENCED_PAGE, > SCAN_PAGE_NULL, > SCAN_SCAN_ABORT, > SCAN_PAGE_COUNT, > @@ -68,6 +68,7 @@ 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 int khugepaged_min_ptes_young __read_mostly; We should set it to 1 to preserve old behavior.