linux-kernel - Re: [RFC PATCH 01/31] mm: migrate: Add exchange

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <749d5674-9e85-1fe9-4a3b-1d6ad06948b4@arm.com>
Date:   Wed, 20 Feb 2019 10:08:36 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Zi Yan <ziy@...dia.com>, Vlastimil Babka <vbabka@...e.cz>,
        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 02/19/2019 06:26 PM, Matthew Wilcox wrote:
> On Tue, Feb 19, 2019 at 01:12:07PM +0530, Anshuman Khandual wrote:
>> But the location of this temp page matters as well because you would like to
>> saturate the inter node interface. It needs to be either of the nodes where
>> the source or destination page belongs. Any other node would generate two
>> internode copy process which is not what you intend here I guess.
> That makes no sense.  It should be allocated on the local node of the CPU
> performing the copy.  If the CPU is in node A, the destination is in node B
> and the source is in node C, then you're doing 4k worth of reads from node C,
> 4k worth of reads from node B, 4k worth of writes to node C followed by
> 4k worth of writes to node B.  Eventually the 4k of dirty cachelines on
> node A will be written back from cache to the local memory (... or not,
> if that page gets reused for some other purpose first).
> 
> If you allocate the page on node B or node C, that's an extra 4k of writes
> to be sent across the inter-node link.

Thats right there will be an extra remote write. My assumption was that the CPU
performing the copy belongs to either node B or node C.