linux-kernel - Re: [PATCH 1/2] sched/wait: Break up long wake list walk

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: <20170822190828.GO32112@worktop.programming.kicks-ass.net>
Date:   Tue, 22 Aug 2017 21:08:28 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "Liang, Kan" <kan.liang@...el.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mel Gorman <mgorman@...e.de>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>, Jan Kara <jack@...e.cz>,
        linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] sched/wait: Break up long wake list walk

On Tue, Aug 22, 2017 at 11:19:12AM -0700, Linus Torvalds wrote:
> And since everybody touches it, as a result everybody eventually
> thinks that page should be migrated to their NUMA node.

So that migration stuff has a filter on, we need two consecutive numa
faults from the same page_cpupid 'hash', see
should_numa_migrate_memory().

And since this appears to be anonymous memory (no THP) this is all a
single address space. However, we don't appear to invalidate TLBs when
we upgrade the PTE protection bits (not strictly required of course), so
we can have multiple CPUs trip over the same 'old' NUMA PTE.

Still, generating such a migration storm would be fairly tricky I think.