linux-kernel - Re: [RFC 0/3] mm: Discard lazily freed pages when migrating

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: <874kuyyu7u.fsf@yhuang-dev.intel.com>
Date:   Mon, 09 Mar 2020 13:26:29 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Mel Gorman <mgorman@...e.de>
Cc:     Michal Hocko <mhocko@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        Vlastimil Babka <vbabka@...e.cz>, Zi Yan <ziy@...dia.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Minchan Kim <minchan@...nel.org>,
        Hugh Dickins <hughd@...gle.com>,
        Alexander Duyck <alexander.duyck@...il.com>
Subject: Re: [RFC 0/3] mm: Discard lazily freed pages when migrating

Mel Gorman <mgorman@...e.de> writes:

> I think the only concrete outcome has been that userspace potentially
> benefits if the total number of MADV_FREE pages is reported
> globally. Even that is marginal as smaps has the information to tell
> the difference between high RSS due to a memory leak and high RSS
> usage due to MADV_FREE. The /proc/vmstats for MADV_FREE are of
> marginal benefit given that they do not tell us much about the current
> number of MADV_FREE pages in the system.

We can implement a counter for MADV_FREE that increases when we
ClearPageSwapBacked() and decrease when we SetPageSwapBacked() for an
anonymous page.  But this cannot count lazily freed pages correctly.
Because when a clean MDV_FREE page becomes dirty, there's no page fault
so we will not be notified.  And you have never run into the MADV_FREE
issues other than the memory leaking debugging...

Best Regards,
Huang, Ying