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s=arc-20220608; d=hostedemail.com; t=1712064168; a=rsa-sha256; cv=none; b=t/QlBn28xDEnu4FotSjZRyBQpPPKeut5sEirXu9KanoQwsj9nzTg5I3zMXkwlvPOSiculf xBwEX8oQRijvGEEX+/jhEvu1Tci2T0LmkvMNlAl15/ALbu7+4nVGbtSPUlRH8KidoggC5M s6H6jA3b102L2kCN0dD03oFzhAGQyEk= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=none; spf=pass (imf18.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com; dmarc=pass (policy=none) header.from=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 8B5BC1007; Tue, 2 Apr 2024 06:23:19 -0700 (PDT) Received: from [10.1.38.163] (XHFQ2J9959.cambridge.arm.com [10.1.38.163]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id EB8EE3F766; Tue, 2 Apr 2024 06:22:45 -0700 (PDT) Message-ID: <47fa11db-3c26-48a6-bb7e-5ea59739b691@arm.com> Date: Tue, 2 Apr 2024 14:22:44 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 5/6] mm: vmscan: Avoid split during shrink_folio_list() Content-Language: en-GB From: Ryan Roberts To: Barry Song <21cnbao@gmail.com> Cc: Andrew Morton , David Hildenbrand , Matthew Wilcox , Huang Ying , Gao Xiang , Yu Zhao , Yang Shi , Michal Hocko , Kefeng Wang , Chris Li , Lance Yang , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Barry Song References: <20240327144537.4165578-1-ryan.roberts@arm.com> <20240327144537.4165578-6-ryan.roberts@arm.com> <63c9caf4-3af4-4149-b3c2-e677788cb11f@arm.com> In-Reply-To: <63c9caf4-3af4-4149-b3c2-e677788cb11f@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: B30011C0008 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: mknjqhohedcfi5mb48mp8wcy548ds7xu X-HE-Tag: 1712064168-672241 X-HE-Meta: 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 QVZG1p20 qGphn1GVmVeSEl16vvqTODI+InTORehCmJa6KZ0G8ntbgZg9i0SIT608HgQYNvI8I0bR651b5wLaOrrHq2yiSsjTtCecK92g/YM1wxy4kPua7CcF+/Hp3J+dPOag2uyjvrCwdDdvilrVjpk5wS0iS6GTRgFRVWZQ02oWrmgAw1rNoAchCWGUkwG5NWVlhNVwv/xzYN0MU7OpuCgacNNrj8MCm0I+3fY9CVl99+iqyse2vkyOzzcJIe4DHH5bFJxCIqNTQWDH1L1/vB1UTo9SixMKzH+P8CBlTTPDP8zaZnR3DCRMm3rcWTeoqm6Vsk3Ym9SRCYw7Ubbgcy4mc+GX1Ut8DyQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 02/04/2024 14:10, Ryan Roberts wrote: > On 28/03/2024 08:18, Barry Song wrote: >> On Thu, Mar 28, 2024 at 3:45 AM Ryan Roberts wrote: >>> >>> Now that swap supports storing all mTHP sizes, avoid splitting large >>> folios before swap-out. This benefits performance of the swap-out path >>> by eliding split_folio_to_list(), which is expensive, and also sets us >>> up for swapping in large folios in a future series. >>> >>> If the folio is partially mapped, we continue to split it since we want >>> to avoid the extra IO overhead and storage of writing out pages >>> uneccessarily. >>> >>> Reviewed-by: David Hildenbrand >>> Reviewed-by: Barry Song >>> Signed-off-by: Ryan Roberts >>> --- >>> mm/vmscan.c | 9 +++++---- >>> 1 file changed, 5 insertions(+), 4 deletions(-) >>> >>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>> index 00adaf1cb2c3..293120fe54f3 100644 >>> --- a/mm/vmscan.c >>> +++ b/mm/vmscan.c >>> @@ -1223,11 +1223,12 @@ static unsigned int shrink_folio_list(struct list_head *folio_list, >>> if (!can_split_folio(folio, NULL)) >>> goto activate_locked; >>> /* >>> - * Split folios without a PMD map right >>> - * away. Chances are some or all of the >>> - * tail pages can be freed without IO. >>> + * Split partially mapped folios right >>> + * away. We can free the unmapped pages >>> + * without IO. >>> */ >>> - if (!folio_entire_mapcount(folio) && >>> + if (data_race(!list_empty( >>> + &folio->_deferred_list)) && >>> split_folio_to_list(folio, >>> folio_list)) >>> goto activate_locked; >> >> Hi Ryan, >> >> Sorry for bringing up another minor issue at this late stage. > > No problem - I'd rather take a bit longer and get it right, rather than rush it > and get it wrong! > >> >> During the debugging of thp counter patch v2, I noticed the discrepancy between >> THP_SWPOUT_FALLBACK and THP_SWPOUT. >> >> Should we make adjustments to the counter? > > Yes, agreed; we want to be consistent here with all the other existing THP > counters; they only refer to PMD-sized THP. I'll make the change for the next > version. > > I guess we will eventually want equivalent counters for per-size mTHP using the > framework you are adding. > >> >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index 293120fe54f3..d7856603f689 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -1241,8 +1241,10 @@ static unsigned int shrink_folio_list(struct >> list_head *folio_list, >> folio_list)) >> goto activate_locked; >> #ifdef CONFIG_TRANSPARENT_HUGEPAGE >> - >> count_memcg_folio_events(folio, THP_SWPOUT_FALLBACK, 1); >> - count_vm_event(THP_SWPOUT_FALLBACK); >> + if (folio_test_pmd_mappable(folio)) { This doesn't quite work because we have already split the folio here, so this will always return false. I've changed it to: if (nr_pages >= HPAGE_PMD_NR) { >> + >> count_memcg_folio_events(folio, THP_SWPOUT_FALLBACK, 1); >> + >> count_vm_event(THP_SWPOUT_FALLBACK); >> + } >> #endif >> if (!add_to_swap(folio)) >> goto activate_locked_split; >> >> >> Because THP_SWPOUT is only for pmd: >> >> static inline void count_swpout_vm_event(struct folio *folio) >> { >> #ifdef CONFIG_TRANSPARENT_HUGEPAGE >> if (unlikely(folio_test_pmd_mappable(folio))) { >> count_memcg_folio_events(folio, THP_SWPOUT, 1); >> count_vm_event(THP_SWPOUT); >> } >> #endif >> count_vm_events(PSWPOUT, folio_nr_pages(folio)); >> } >> >> I can provide per-order counters for this in my THP counter patch. >> >>> -- >>> 2.25.1 >>> >> >> Thanks >> Barry >