linux-kernel - Re: [PATCH v3 RFC 14/14] mm: speedup page alloc for MPOL_PREFERRED_MANY by adding a NO

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:   Wed, 3 Mar 2021 08:31:41 -0800
From:   Ben Widawsky <ben.widawsky@...el.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Feng Tang <feng.tang@...el.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        Andi leen <ak@...ux.intel.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>
Subject: Re: [PATCH v3 RFC 14/14] mm: speedup page alloc for
 MPOL_PREFERRED_MANY by adding a NO_SLOWPATH gfp bit

On 21-03-03 14:59:35, Michal Hocko wrote:
> On Wed 03-03-21 21:46:44, Feng Tang wrote:
> > On Wed, Mar 03, 2021 at 09:18:32PM +0800, Tang, Feng wrote:
> > > On Wed, Mar 03, 2021 at 01:32:11PM +0100, Michal Hocko wrote:
> > > > On Wed 03-03-21 20:18:33, Feng Tang wrote:
> [...]
> > > > > One thing I tried which can fix the slowness is:
> > > > > 
> > > > > +	gfp_mask &= ~(__GFP_DIRECT_RECLAIM | __GFP_KSWAPD_RECLAIM);
> > > > > 
> > > > > which explicitly clears the 2 kinds of reclaim. And I thought it's too
> > > > > hacky and didn't mention it in the commit log.
> > > > 
> > > > Clearing __GFP_DIRECT_RECLAIM would be the right way to achieve
> > > > GFP_NOWAIT semantic. Why would you want to exclude kswapd as well? 
> > > 
> > > When I tried gfp_mask &= ~__GFP_DIRECT_RECLAIM, the slowness couldn't
> > > be fixed.
> > 
> > I just double checked by rerun the test, 'gfp_mask &= ~__GFP_DIRECT_RECLAIM'
> > can also accelerate the allocation much! though is still a little slower than
> > this patch. Seems I've messed some of the tries, and sorry for the confusion!
> > 
> > Could this be used as the solution? or the adding another fallback_nodemask way?
> > but the latter will change the current API quite a bit.
> 
> I haven't got to the whole series yet. The real question is whether the
> first attempt to enforce the preferred mask is a general win. I would
> argue that it resembles the existing single node preferred memory policy
> because that one doesn't push heavily on the preferred node either. So
> dropping just the direct reclaim mode makes some sense to me.
> 
> IIRC this is something I was recommending in an early proposal of the
> feature.

My assumption [FWIW] is that the usecases we've outlined for multi-preferred
would want more heavy pushing on the preference mask. However, maybe the uapi
could dictate how hard to try/not try.