linux-kernel - Re: [v3 0/9] parallelized "struct page" zeroing

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Message-ID: <20170531163131.GY27783@dhcp22.suse.cz>
Date:   Wed, 31 May 2017 18:31:31 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Pasha Tatashin <pasha.tatashin@...cle.com>
Cc:     linux-kernel@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, borntraeger@...ibm.com,
        heiko.carstens@...ibm.com, davem@...emloft.net
Subject: Re: [v3 0/9] parallelized "struct page" zeroing

On Tue 30-05-17 13:16:50, Pasha Tatashin wrote:
> >Could you be more specific? E.g. how are other stores done in
> >__init_single_page safe then? I am sorry to be dense here but how does
> >the full 64B store differ from other stores done in the same function.
> 
> Hi Michal,
> 
> It is safe to do regular 8-byte and smaller stores (stx, st, sth, stb)
> without membar, but they are slower compared to STBI which require a membar
> before memory can be accessed.

OK, so why cannot we make zero_struct_page 8x 8B stores, other arches
would do memset. You said it would be slower but would that be
measurable? I am sorry to be so persistent here but I would be really
happier if this didn't depend on the deferred initialization. If this is
absolutely a no-go then I can live with that of course.

-- 
Michal Hocko
SUSE Labs