linux-kernel - Re: [PATCH -v2 1/2] mm, swap: Use kvzalloc to allocate some swap data structure

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:   Fri, 24 Mar 2017 09:52:11 -0700
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...ux.intel.com>,
        John Hubbard <jhubbard@...dia.com>,
        "Huang, Ying" <ying.huang@...el.com>
Cc:     David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andi Kleen <ak@...ux.intel.com>, Shaohua Li <shli@...nel.org>,
        Rik van Riel <riel@...hat.com>,
        Michal Hocko <mhocko@...e.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Aaron Lu <aaron.lu@...el.com>,
        Gerald Schaefer <gerald.schaefer@...ibm.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Hugh Dickins <hughd@...gle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Vegard Nossum <vegard.nossum@...cle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH -v2 1/2] mm, swap: Use kvzalloc to allocate some swap
 data structure

On Fri, 2017-03-24 at 06:56 -0700, Dave Hansen wrote:
> On 03/24/2017 12:33 AM, John Hubbard wrote:
> > 
> > There might be some additional information you are using to come up with
> > that conclusion, that is not obvious to me. Any thoughts there? These
> > calls use the same underlying page allocator (and I thought that both
> > were subject to the same constraints on defragmentation, as a result of
> > that). So I am not seeing any way that kmalloc could possibly be a
> > less-fragmenting call than vmalloc.
> You guys are having quite a discussion over a very small point.
> 
> But, Ying is right.
> 
> Let's say we have a two-page data structure.  vmalloc() takes two
> effectively random order-0 pages, probably from two different 2M pages
> and pins them.  That "kills" two 2M pages.
> 
> kmalloc(), allocating two *contiguous* pages, is very unlikely to cross
> a 2M boundary (it theoretically could).  That means it will only "kill"
> the possibility of a single 2M page.  More 2M pages == less fragmentation.

In vmalloc, it eventually calls __vmalloc_area_node that allocates the
page one at a time.  There's no attempt there to make the pages contiguous
if I am reading the code correctly.  So that will increase the memory
fragmentation as we will be piecing together pages from all over the places.  

Tim