linux-kernel - Re: [PATCH] mm: Fix comment for NODEMASK

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Message-ID: <20180821125846.GB9489@techadventures.net>
Date:   Tue, 21 Aug 2018 14:58:46 +0200
From:   Oscar Salvador <osalvador@...hadventures.net>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, tglx@...utronix.de,
        joe@...ches.com, arnd@...db.de, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH] mm: Fix comment for NODEMASK_ALLOC

On Tue, Aug 21, 2018 at 02:51:56PM +0200, Michal Hocko wrote:
> On Tue 21-08-18 14:30:24, Oscar Salvador wrote:
> > On Tue, Aug 21, 2018 at 02:17:34PM +0200, Michal Hocko wrote:
> > > We do have CONFIG_NODES_SHIFT=10 in our SLES kernels for quite some
> > > time (around SLE11-SP3 AFAICS).
> > > 
> > > Anyway, isn't NODES_ALLOC over engineered a bit? Does actually even do
> > > larger than 1024 NUMA nodes? This would be 128B and from a quick glance
> > > it seems that none of those functions are called in deep stacks. I
> > > haven't gone through all of them but a patch which checks them all and
> > > removes NODES_ALLOC would be quite nice IMHO.
> > 
> > No, maximum we can get is 1024 NUMA nodes.
> > I checked this when writing another patch [1], and since having gone
> > through all archs Kconfigs, CONFIG_NODES_SHIFT=10 is the limit.
> > 
> > NODEMASK_ALLOC gets only called from:
> > 
> > - unregister_mem_sect_under_nodes() (not anymore after [1])
> > - __nr_hugepages_store_common (This does not seem to have a deep stack, we could use a normal nodemask_t)
> > 
> > But is also used for NODEMASK_SCRATCH (mainly used for mempolicy):
> 
> mempolicy code should be a shallow stack as well. Mostly the syscall
> entry.

Ok, then I could give it a try and see if we can get rid of NODEMASK_ALLOC in there
as well.

-- 
Oscar Salvador
SUSE L3