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Date: Mon, 18 Feb 2019 09:51:33 -0800 From: Zi Yan <ziy@...dia.com> To: Vlastimil Babka <vbabka@...e.cz> CC: Matthew Wilcox <willy@...radead.org>, <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>, Dave Hansen <dave.hansen@...ux.intel.com>, Michal Hocko <mhocko@...nel.org>, "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>, Andrew Morton <akpm@...ux-foundation.org>, Mel Gorman <mgorman@...hsingularity.net>, John Hubbard <jhubbard@...dia.com>, Mark Hairgrove <mhairgrove@...dia.com>, Nitin Gupta <nigupta@...dia.com>, David Nellans <dnellans@...dia.com> Subject: Re: [RFC PATCH 01/31] mm: migrate: Add exchange_pages to exchange two lists of pages. On 18 Feb 2019, at 9:42, Vlastimil Babka wrote: > On 2/18/19 6:31 PM, Zi Yan wrote: >> The purpose of proposing exchange_pages() is to avoid allocating any >> new >> page, >> so that we would not trigger any potential page reclaim or memory >> compaction. >> Allocating a temporary page defeats the purpose. > > Compaction can only happen for order > 0 temporary pages. Even if you > used > single order = 0 page to gradually exchange e.g. a THP, it should be > better than > u64. Allocating order = 0 should be a non-issue. If it's an issue, > then the > system is in a bad state and physically contiguous layout is a > secondary concern. You are right if we only need to allocate one order-0 page. But this also means we can only exchange two pages at a time. We need to add a lock to make sure the temporary page is used exclusively or we need to keep allocating temporary pages when multiple exchange_pages() are happening at the same time. -- Best Regards, Yan Zi
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