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Mon, 29 Jun 2020 23:37:42 +0000 (UTC) IronPort-SDR: 65uLAcorIQvmY1MjqGL4ST8BEIqZ8F82gzjvxL1qsbU9oxZESOXlYNIGtu+xjazODAV3g+rw7j P8t6iyQRX96w== X-IronPort-AV: E=McAfee;i="6000,8403,9666"; a="146089931" X-IronPort-AV: E=Sophos;i="5.75,296,1589266800"; d="scan'208";a="146089931" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Jun 2020 16:37:40 -0700 IronPort-SDR: CDjs5miLLIZgGZ19yf5Yq8QdITReIs4RNN8/PqXo+b3RAooRc1pBLoRJ/WzT7WnNeQkYQPomw1 C4Y2YmmTRAFA== X-IronPort-AV: E=Sophos;i="5.75,296,1589266800"; d="scan'208";a="454378949" Received: from tclumbax-mobl2.gar.corp.intel.com (HELO [10.255.1.194]) ([10.255.1.194]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Jun 2020 16:37:38 -0700 Subject: Re: [PATCH] mm/vmscan: restore zone_reclaim_mode ABI To: Baoquan He Cc: Dave Hansen , linux-kernel@vger.kernel.org, linux-mm@kvack.org, ben.widawsky@intel.com, alex.shi@linux.alibaba.com, dwagner@suse.de, tobin@kernel.org, cl@linux.com, akpm@linux-foundation.org, stable@kernel.org References: <20200626003459.D8E015CA@viggo.jf.intel.com> <20200629065203.GJ3346@MiWiFi-R3L-srv> <3ba94f19-3b18-9d52-a070-f652620c88e6@intel.com> <20200629233043.GK3346@MiWiFi-R3L-srv> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200629233043.GK3346@MiWiFi-R3L-srv> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 11267180B3AA7 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 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: On 6/29/20 4:30 PM, Baoquan He wrote: >> The only way I can plausibly think of "cleaning up" the RECLAIM_ZONE bit >> would be to raise our confidence that it is truly unused. That takes >> time, and probably a warning if we see it being set. If we don't run >> into anybody setting it or depending on it being set in a few years, we >> can remove it. > So adding the old bit back for compatibility looks good, thanks. > > Then we have to be very careful when adding and reviewing new > interface introducing, should not leave one which might be used > in the future. > > In fact, RECLAIM_ZONE is not completely useless. At least, when the old > bit 0 is set, it may enter into node_reclaim() in get_page_from_freelist(), > that makes it like a switch. > > get_page_from_freelist { > > ... > if (node_reclaim_mode == 0 || > !zone_allows_reclaim(ac->preferred_zoneref->zone, zone)) > continue; > ... > } Oh, that's a very good point. There are a couple of those around. Let me circle back and update the documentation and the variable name. I'll send out another version.