linux-kernel - RE: [PATCH v10 09/10] mm: stop zeroing memory during allocation in vmemmap

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6DD008BB4D@AcuExch.aculab.com>
Date:   Fri, 6 Oct 2017 12:11:42 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Michal Hocko' <mhocko@...nel.org>
CC:     'Pavel Tatashin' <pasha.tatashin@...cle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
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Subject: RE: [PATCH v10 09/10] mm: stop zeroing memory during allocation in
 vmemmap

From: Michal Hocko
> Sent: 06 October 2017 12:47
> On Fri 06-10-17 11:10:14, David Laight wrote:
> > From: Pavel Tatashin
> > > Sent: 05 October 2017 22:11
> > > vmemmap_alloc_block() will no longer zero the block, so zero memory
> > > at its call sites for everything except struct pages.  Struct page memory
> > > is zero'd by struct page initialization.
> >
> > It seems dangerous to change an allocator to stop zeroing memory.
> > It is probably saver to add a new function that doesn't zero
> > the memory and use that is the places where you don't want it
> > to be zeroed.
> 
> Not sure what you mean. memblock_virt_alloc_try_nid_raw is a new
> function which doesn't zero out...

You should probably leave vmemap_alloc_block() zeroing the memory
so that existing alls don't have to be changed - apart from the
ones you are explicitly optimising.

	David