linux-kernel - Re: [PATCH] mm: always consider THP when adjusting min_free

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]

Date:   Thu, 6 Feb 2020 12:39:45 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Song Liu <songliubraving@...com>,
        "Kirill A.Shutemov" <kirill.shutemov@...ux.intel.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] mm: always consider THP when adjusting min_free_kbytes

On Wed, Feb 05, 2020 at 05:36:44PM -0800, Mike Kravetz wrote:
> The value of min_free_kbytes is calculated in two routines:
> 1) init_per_zone_wmark_min based on available memory
> 2) set_recommended_min_free_kbytes may reserve extra space for
>    THP allocations
> 
> In both of these routines, a user defined min_free_kbytes value will
> be overwritten if the value calculated in the code is larger. No message
> is logged if the user value is overwritten.
> 
> Change code to never overwrite user defined value.  However, do log a
> message (once per value) showing the value calculated in code.

But what if the user set min_free_kbytes to, say, half of system memory,
and then hot-unplugs three quarters of their memory?  I think the kernel
should protect itself against such foolishness.