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Date:   Wed, 7 Jul 2021 10:42:29 +0200
From:   Michal Hocko <mhocko@suse.com>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     "Uladzislau Rezki (Sony)" <urezki@gmail.com>, linux-mm@kvack.org,
        LKML <linux-kernel@vger.kernel.org>,
        Mel Gorman <mgorman@suse.de>,
        Christoph Hellwig <hch@infradead.org>,
        Matthew Wilcox <willy@infradead.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        Hillf Danton <hdanton@sina.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH v2 1/2] mm/vmalloc: Use batched page requests in
 bulk-allocator
Message-ID: <YOVo9bBtncG3/uLi@dhcp22.suse.cz>
References: <20210705170537.43060-1-urezki@gmail.com>
 <20210706132653.8374852963b25989e360d599@linux-foundation.org>
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On Tue 06-07-21 13:26:53, Andrew Morton wrote:
> On Mon,  5 Jul 2021 19:05:36 +0200 "Uladzislau Rezki (Sony)" <urezki@gmail.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@gmail.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