linux-kernel - Re: [PATCH v2 1/2] mm/vmalloc: Use batched page requests in bulk-allocator

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Date:   Wed, 7 Jul 2021 10:42:29 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     "Uladzislau Rezki (Sony)" <urezki@...il.com>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...e.de>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Hillf Danton <hdanton@...a.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v2 1/2] mm/vmalloc: Use batched page requests in
 bulk-allocator

On Tue 06-07-21 13:26:53, Andrew Morton wrote:
> On Mon,  5 Jul 2021 19:05:36 +0200 "Uladzislau Rezki (Sony)" <urezki@...il.com> wrote:
> 
> > In case of simultaneous vmalloc allocations, for example it is 1GB and
> > 12 CPUs my system is able to hit "BUG: soft lockup" for !CONFIG_PREEMPT
> > kernel.
> > 
> > <snip>
> > ...
> >
> > are obtained, i.e. do batched page requests adding cond_resched() meanwhile
> > to reschedule. Batched value is hard-coded and is 100 pages per call.
> > 
> > Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> 
> Can we please have a Fixes: for this?

Is this a fix for any actual real life problem? I mean allocating 1GB of
vmalloc space back and forth sounds like a stretch to me.
 
> Is this fix important enough for 4.14-rcx?  I think so...

I do not think so. This is an improvement so that vmalloc behaves more
sanely for those abusers...
-- 
Michal Hocko
SUSE Labs