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s=arc-20220608; d=hostedemail.com; t=1692581472; a=rsa-sha256; cv=none; b=o2kTC0gYt+8eFhzpmgADlyOe/QKYSJ0S0WdBwYBbtF80ZO86nWMBG74BnMwZBP2mFcFT/v sDwagnEJ4EgQsoWV3uU1yzoA+5U+F/5hITewmhC0Hk6yYYgVmFcTGmJdjRWd5eApKOSwwJ Entvzxf5308NJDQufF/KB1vrIJfBo2o= ARC-Authentication-Results: i=1; imf15.hostedemail.com; dkim=none; spf=pass (imf15.hostedemail.com: domain of byungchul@sk.com designates 166.125.252.92 as permitted sender) smtp.mailfrom=byungchul@sk.com; dmarc=none X-AuditID: a67dfc5b-d6dff70000001748-a6-64e2be5bc41e Date: Mon, 21 Aug 2023 10:28:05 +0900 From: Byungchul Park To: "Huang, Ying" Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel_team@skhynix.com, akpm@linux-foundation.org, namit@vmware.com, xhao@linux.alibaba.com, mgorman@techsingularity.net, hughd@google.com, willy@infradead.org, david@redhat.com, peterz@infradead.org, luto@kernel.org, dave.hansen@linux.intel.com Subject: Re: [RFC 2/2] mm: Defer TLB flush by keeping both src and dst folios at migration Message-ID: <20230821012804.GA43847@system.software.com> References: <20230804061850.21498-1-byungchul@sk.com> <20230804061850.21498-3-byungchul@sk.com> <877cpx9jsx.fsf@yhuang6-desk2.ccr.corp.intel.com> <20230816001307.GA44941@system.software.com> <87r0o37qcn.fsf@yhuang6-desk2.ccr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; 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Otherwise, no doubt the folio might get messed up. > >> > > >> > To achieve that: > >> > > >> > 1. For the folios that have only non-writable TLB entries, prevent > >> > TLB flush by keeping both source and destination of folios during > >> > migration, which will be handled later at a better time. > >> > > >> > 2. When any non-writable TLB entry changes to writable e.g. through > >> > fault handler, give up CONFIG_MIGRC mechanism so as to perform > >> > TLB flush required right away. > >> > > >> > 3. TLB flushes can be skipped if all TLB flushes required to free the > >> > duplicated folios have been done by any reason, which doesn't have > >> > to be done from migrations. > >> > > >> > 4. Adjust watermark check routine, __zone_watermark_ok(), with the > >> > number of duplicated folios because those folios can be freed > >> > and obtained right away through appropreate TLB flushes. > >> > > >> > 5. Perform TLB flushes and free the duplicated folios pending the > >> > flushes if page allocation routine is in trouble due to memory > >> > pressure, even more aggresively for high order allocation. > >> > >> Is the optimization restricted for page migration only? Can it be used > >> for other places? Like page reclaiming? > > > > Just to make sure, are you talking about the (5) description? For now, > > it's performed at the beginning of __alloc_pages_slowpath(), say, before > > page recaiming. Do you think it'd be meaningful to perform it during page > > reclaiming? Or do you mean something else? > > Not for (5). TLB needs to be flushed during page reclaiming too. Can > similar method be used to reduce TLB flushing there too? If you were talking about unmapping for swap while reclaiming, then I think yes. The case can also take benefit from CONFIG_MIGRC. Byungchul