From: David Miller <davem@davemloft.net>
To: willy@infradead.org
Cc: mhocko@kernel.org, pasha.tatashin@oracle.com,
linux-kernel@vger.kernel.org, sparclinux@vger.kernel.org,
linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org,
linux-s390@vger.kernel.org, borntraeger@de.ibm.com,
heiko.carstens@de.ibm.com
Subject: Re: [v3 0/9] parallelized "struct page" zeroing
Date: Wed, 10 May 2017 14:00:26 -0400 (EDT) [thread overview]
Message-ID: <20170510.140026.1367439672848112283.davem@davemloft.net> (raw)
In-Reply-To: <20170510171703.GC1590@bombadil.infradead.org>
From: Matthew Wilcox <willy@infradead.org>
Date: Wed, 10 May 2017 10:17:03 -0700
> On Wed, May 10, 2017 at 11:19:43AM -0400, David Miller wrote:
>> From: Michal Hocko <mhocko@kernel.org>
>> Date: Wed, 10 May 2017 16:57:26 +0200
>>
>> > Have you measured that? I do not think it would be super hard to
>> > measure. I would be quite surprised if this added much if anything at
>> > all as the whole struct page should be in the cache line already. We do
>> > set reference count and other struct members. Almost nobody should be
>> > looking at our page at this time and stealing the cache line. On the
>> > other hand a large memcpy will basically wipe everything away from the
>> > cpu cache. Or am I missing something?
>>
>> I guess it might be clearer if you understand what the block
>> initializing stores do on sparc64. There are no memory accesses at
>> all.
>>
>> The cpu just zeros out the cache line, that's it.
>>
>> No L3 cache line is allocated. So this "wipe everything" behavior
>> will not happen in the L3.
>
> There's either something wrong with your explanation or my reading
> skills :-)
>
> "There are no memory accesses"
> "No L3 cache line is allocated"
>
> You can have one or the other ... either the CPU sends a cacheline-sized
> write of zeroes to memory without allocating an L3 cache line (maybe
> using the store buffer?), or the CPU allocates an L3 cache line and sets
> its contents to zeroes, probably putting it in the last way of the set
> so it's the first thing to be evicted if not touched.
There is no conflict in what I said.
Only an L2 cache line is allocated and cleared. L3 is left alone.
next prev parent reply other threads:[~2017-05-10 18:00 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-05 17:03 [v3 0/9] parallelized "struct page" zeroing Pavel Tatashin
2017-05-05 17:03 ` [v3 1/9] sparc64: simplify vmemmap_populate Pavel Tatashin
2017-05-05 17:03 ` [v3 2/9] mm: defining memblock_virt_alloc_try_nid_raw Pavel Tatashin
2017-05-05 17:03 ` [v3 3/9] mm: add "zero" argument to vmemmap allocators Pavel Tatashin
2017-05-13 19:17 ` kbuild test robot
2017-05-05 17:03 ` [v3 4/9] mm: do not zero vmemmap_buf Pavel Tatashin
2017-05-05 17:03 ` [v3 5/9] mm: zero struct pages during initialization Pavel Tatashin
2017-05-05 17:03 ` [v3 6/9] sparc64: teach sparc not to zero struct pages memory Pavel Tatashin
2017-05-05 17:03 ` [v3 7/9] x86: teach x86 " Pavel Tatashin
2017-05-05 17:03 ` [v3 8/9] powerpc: teach platforms " Pavel Tatashin
2017-05-05 17:03 ` [v3 9/9] s390: " Pavel Tatashin
2017-05-08 11:36 ` Heiko Carstens
2017-05-15 18:24 ` Pasha Tatashin
2017-05-15 23:17 ` Heiko Carstens
2017-05-16 0:33 ` Pasha Tatashin
2017-05-09 18:12 ` [v3 0/9] parallelized "struct page" zeroing Michal Hocko
2017-05-09 18:54 ` Pasha Tatashin
2017-05-10 7:24 ` Michal Hocko
2017-05-10 13:42 ` Pasha Tatashin
2017-05-10 14:57 ` Michal Hocko
2017-05-10 15:01 ` Pasha Tatashin
2017-05-10 15:20 ` David Miller
2017-05-11 20:47 ` Pasha Tatashin
2017-05-11 20:59 ` Pasha Tatashin
2017-05-12 16:57 ` David Miller
2017-05-12 17:24 ` Pasha Tatashin
2017-05-12 17:37 ` David Miller
2017-05-16 23:50 ` Benjamin Herrenschmidt
2017-05-12 16:56 ` David Miller
2017-05-10 15:19 ` David Miller
2017-05-10 17:17 ` Matthew Wilcox
2017-05-10 18:00 ` David Miller [this message]
2017-05-10 21:11 ` Matthew Wilcox
2017-05-11 8:05 ` Michal Hocko
2017-05-11 14:35 ` David Miller
2017-05-15 18:12 ` Pasha Tatashin
2017-05-15 19:38 ` Michal Hocko
2017-05-15 20:44 ` Pasha Tatashin
2017-05-16 8:36 ` Michal Hocko
2017-05-26 16:45 ` Pasha Tatashin
2017-05-29 11:53 ` Michal Hocko
2017-05-30 17:16 ` Pasha Tatashin
2017-05-31 16:31 ` Michal Hocko
2017-05-31 16:51 ` David Miller
2017-06-01 3:35 ` Pasha Tatashin
2017-06-01 8:46 ` Michal Hocko
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