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X-IronPort-AV: E=McAfee;i="6600,9927,10741"; a="387217426" X-IronPort-AV: E=Sophos;i="6.00,243,1681196400"; d="scan'208";a="387217426" Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Jun 2023 20:24:40 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10741"; a="959008686" X-IronPort-AV: E=Sophos;i="6.00,243,1681196400"; d="scan'208";a="959008686" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.238.208.55]) by fmsmga006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Jun 2023 20:24:37 -0700 From: "Huang, Ying" To: Mel Gorman , Cc: Baolin Wang , , , , Subject: Re: [PATCH v2] mm: compaction: skip memory hole rapidly when isolating migratable pages References: <770f9f61472b24b6bc89adbd71a77d9cf62bb54f.1686646361.git.baolin.wang@linux.alibaba.com> <20230614095501.m4porztaibchrgwx@techsingularity.net> Date: Thu, 15 Jun 2023 11:22:58 +0800 In-Reply-To: <20230614095501.m4porztaibchrgwx@techsingularity.net> (Mel Gorman's message of "Wed, 14 Jun 2023 10:55:01 +0100") Message-ID: <87ilbpo1d9.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: C2AD380004 X-Stat-Signature: 7q1h6w41877st6ybyig5rbwnt57es5q3 X-HE-Tag: 1686799482-952385 X-HE-Meta: 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 goD79VAz sCbav0XcbBCp6Xhq79G1520Bk8v/GVAtFtmPCFGMbTKxUZYgqb/pgsX4dx+82tNFgcoLewTgWsOr0UTwNNNi7TkEVYnRsR+zN/Hn4qkDrmAMJZSi+Vt+yMVBW6JvCRciHPvbJYDt43xIxAM+K23LXtT6sG9QM6SuB0LQtJyhlryHrFlOqh+rI7usWCQX5m5+zmKLQAmCIDkW3RY6RFQNbhPW8eE4MzsL/RSZv 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: Hi, Mel, Mel Gorman writes: > On Tue, Jun 13, 2023 at 04:55:04PM +0800, Baolin Wang wrote: >> On some machines, the normal zone can have a large memory hole like >> below memory layout, and we can see the range from 0x100000000 to >> 0x1800000000 is a hole. So when isolating some migratable pages, the >> scanner can meet the hole and it will take more time to skip the large >> hole. From my measurement, I can see the isolation scanner will take >> 80us ~ 100us to skip the large hole [0x100000000 - 0x1800000000]. >> >> So adding a new helper to fast search next online memory section >> to skip the large hole can help to find next suitable pageblock >> efficiently. With this patch, I can see the large hole scanning only >> takes < 1us. >> >> [ 0.000000] Zone ranges: >> [ 0.000000] DMA [mem 0x0000000040000000-0x00000000ffffffff] >> [ 0.000000] DMA32 empty >> [ 0.000000] Normal [mem 0x0000000100000000-0x0000001fa7ffffff] >> [ 0.000000] Movable zone start for each node >> [ 0.000000] Early memory node ranges >> [ 0.000000] node 0: [mem 0x0000000040000000-0x0000000fffffffff] >> [ 0.000000] node 0: [mem 0x0000001800000000-0x0000001fa3c7ffff] >> [ 0.000000] node 0: [mem 0x0000001fa3c80000-0x0000001fa3ffffff] >> [ 0.000000] node 0: [mem 0x0000001fa4000000-0x0000001fa402ffff] >> [ 0.000000] node 0: [mem 0x0000001fa4030000-0x0000001fa40effff] >> [ 0.000000] node 0: [mem 0x0000001fa40f0000-0x0000001fa73cffff] >> [ 0.000000] node 0: [mem 0x0000001fa73d0000-0x0000001fa745ffff] >> [ 0.000000] node 0: [mem 0x0000001fa7460000-0x0000001fa746ffff] >> [ 0.000000] node 0: [mem 0x0000001fa7470000-0x0000001fa758ffff] >> [ 0.000000] node 0: [mem 0x0000001fa7590000-0x0000001fa7ffffff] >> >> Signed-off-by: Baolin Wang > > This may only be necessary for non-contiguous zones so a check for > zone_contiguous could be made but I suspect the saving, if any, would be > marginal. > > However, it's subtle that block_end_pfn can end up in an arbirary location > past the end of the zone or past cc->free_pfn. As the "continue" will update > cc->migrate_pfn, that might lead to errors in the future. It would be a > lot safer to pass in cc->free_pfn and do two things with the value. First, > there is no point scanning for a valid online section past cc->free_pfn so > terminating after cc->free_pfn may save some cycles. Second, cc->migrate_pfn > does not end up with an arbitrary value which is a more defensive approach > to any future programming errors. I have thought about this before. Originally, I had thought that we were safe because cc->free_pfn should be in a online section and block_end_pfn should reach cc->free_pfn before the end of zone. But after checking more code and thinking about it again, I found that the underlying sections may go offline under us during compaction. So that, cc->free_pfn may be in a offline section or after the end of zone. So, you are right, we need to consider the range of block_end_pfn. But, if we thought in this way (memory online/offline at any time), it appears that we need to check whether the underlying section was offlined. For example, is it safe to use "pfn_to_page()" in "isolate_migratepages_block()"? Is it possible for the underlying section to be offlined under us? Hi, David, can you teach me on this too? Best Regards, Huang, Ying