From: Alexander Duyck <alexander.h.duyck@linux.intel.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-mm@kvack.org, akpm@linux-foundation.org,
pavel.tatashin@microsoft.com, dave.jiang@intel.com,
linux-kernel@vger.kernel.org, willy@infradead.org,
davem@davemloft.net, yi.z.zhang@linux.intel.com,
khalid.aziz@oracle.com, rppt@linux.vnet.ibm.com, vbabka@suse.cz,
sparclinux@vger.kernel.org, dan.j.williams@intel.com,
ldufour@linux.vnet.ibm.com, mgorman@techsingularity.net,
mingo@kernel.org, kirill.shutemov@linux.intel.com
Subject: Re: [mm PATCH v3 1/6] mm: Use mm_zero_struct_page from SPARC on all 64b architectures
Date: Wed, 17 Oct 2018 08:07:06 -0700 [thread overview]
Message-ID: <9700b00f-a8a4-e318-f6a8-71fd1e7021b3@linux.intel.com> (raw)
In-Reply-To: <20181017084744.GH18839@dhcp22.suse.cz>
On 10/17/2018 1:47 AM, Michal Hocko wrote:
> On Mon 15-10-18 13:26:56, Alexander Duyck wrote:
>> This change makes it so that we use the same approach that was already in
>> use on Sparc on all the archtectures that support a 64b long.
>>
>> This is mostly motivated by the fact that 8 to 10 store/move instructions
>> are likely always going to be faster than having to call into a function
>> that is not specialized for handling page init.
>>
>> An added advantage to doing it this way is that the compiler can get away
>> with combining writes in the __init_single_page call. As a result the
>> memset call will be reduced to only about 4 write operations, or at least
>> that is what I am seeing with GCC 6.2 as the flags, LRU poitners, and
>> count/mapcount seem to be cancelling out at least 4 of the 8 assignments on
>> my system.
>>
>> One change I had to make to the function was to reduce the minimum page
>> size to 56 to support some powerpc64 configurations.
>
> This really begs for numbers. I do not mind the change itself with some
> minor comments below.
>
> [...]
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index bb0de406f8e7..ec6e57a0c14e 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -102,8 +102,42 @@ static inline void set_max_mapnr(unsigned long limit) { }
>> * zeroing by defining this macro in <asm/pgtable.h>.
>> */
>> #ifndef mm_zero_struct_page
>
> Do we still need this ifdef? I guess we can wait for an arch which
> doesn't like this change and then add the override. I would rather go
> simple if possible.
We probably don't, but as soon as I remove it somebody will probably
complain somewhere. I guess I could drop it for now and see if anybody
screams. Adding it back should be pretty straight forward since it would
only be 2 lines.
>> +#if BITS_PER_LONG == 64
>> +/* This function must be updated when the size of struct page grows above 80
>> + * or reduces below 64. The idea that compiler optimizes out switch()
>> + * statement, and only leaves move/store instructions
>> + */
>> +#define mm_zero_struct_page(pp) __mm_zero_struct_page(pp)
>> +static inline void __mm_zero_struct_page(struct page *page)
>> +{
>> + unsigned long *_pp = (void *)page;
>> +
>> + /* Check that struct page is either 56, 64, 72, or 80 bytes */
>> + BUILD_BUG_ON(sizeof(struct page) & 7);
>> + BUILD_BUG_ON(sizeof(struct page) < 56);
>> + BUILD_BUG_ON(sizeof(struct page) > 80);
>> +
>> + switch (sizeof(struct page)) {
>> + case 80:
>> + _pp[9] = 0; /* fallthrough */
>> + case 72:
>> + _pp[8] = 0; /* fallthrough */
>> + default:
>> + _pp[7] = 0; /* fallthrough */
>> + case 56:
>> + _pp[6] = 0;
>> + _pp[5] = 0;
>> + _pp[4] = 0;
>> + _pp[3] = 0;
>> + _pp[2] = 0;
>> + _pp[1] = 0;
>> + _pp[0] = 0;
>> + }
>
> This just hit my eyes. I have to confess I have never seen default: to
> be not the last one in the switch. Can we have case 64 instead or does gcc
> complain? I would be surprised with the set of BUILD_BUG_ONs.
I can probably just replace the "default:" with "case 64:". I think I
have seen other switch statements in the kernel without a default so
odds are it should be okay.
next prev parent reply other threads:[~2018-10-17 15:07 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-15 20:26 [mm PATCH v3 0/6] Deferred page init improvements Alexander Duyck
2018-10-15 20:26 ` [mm PATCH v3 1/6] mm: Use mm_zero_struct_page from SPARC on all 64b architectures Alexander Duyck
2018-10-16 19:01 ` Pavel Tatashin
2018-10-17 7:30 ` Mike Rapoport
2018-10-17 14:52 ` Alexander Duyck
2018-10-17 8:47 ` Michal Hocko
2018-10-17 15:07 ` Alexander Duyck [this message]
2018-10-17 15:12 ` Pavel Tatashin
2018-10-17 15:40 ` David Laight
2018-10-17 16:31 ` Alexander Duyck
2018-10-17 17:08 ` Pavel Tatashin
2018-10-17 16:34 ` Michal Hocko
2018-10-15 20:27 ` [mm PATCH v3 2/6] mm: Drop meminit_pfn_in_nid as it is redundant Alexander Duyck
2018-10-16 20:33 ` Pavel Tatashin
2018-10-16 20:49 ` Alexander Duyck
2018-10-16 21:06 ` Pavel Tatashin
2018-10-17 9:04 ` Michal Hocko
2018-10-15 20:27 ` [mm PATCH v3 3/6] mm: Use memblock/zone specific iterator for handling deferred page init Alexander Duyck
2018-10-17 9:11 ` Michal Hocko
2018-10-17 15:17 ` Alexander Duyck
2018-10-17 16:42 ` Mike Rapoport
2018-10-15 20:27 ` [mm PATCH v3 4/6] mm: Move hot-plug specific memory init into separate functions and optimize Alexander Duyck
2018-10-17 9:18 ` Michal Hocko
2018-10-17 15:26 ` Alexander Duyck
2018-10-24 12:36 ` Michal Hocko
2018-10-24 15:08 ` Alexander Duyck
2018-10-24 15:27 ` Michal Hocko
2018-10-24 17:35 ` Alexander Duyck
2018-10-25 12:41 ` Michal Hocko
2018-10-15 20:27 ` [mm PATCH v3 5/6] mm: Use common iterator for deferred_init_pages and deferred_free_pages Alexander Duyck
2018-10-15 20:27 ` [mm PATCH v3 6/6] mm: Add reserved flag setting to set_page_links Alexander Duyck
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=9700b00f-a8a4-e318-f6a8-71fd1e7021b3@linux.intel.com \
--to=alexander.h.duyck@linux.intel.com \
--cc=akpm@linux-foundation.org \
--cc=dan.j.williams@intel.com \
--cc=dave.jiang@intel.com \
--cc=davem@davemloft.net \
--cc=khalid.aziz@oracle.com \
--cc=kirill.shutemov@linux.intel.com \
--cc=ldufour@linux.vnet.ibm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mgorman@techsingularity.net \
--cc=mhocko@kernel.org \
--cc=mingo@kernel.org \
--cc=pavel.tatashin@microsoft.com \
--cc=rppt@linux.vnet.ibm.com \
--cc=sparclinux@vger.kernel.org \
--cc=vbabka@suse.cz \
--cc=willy@infradead.org \
--cc=yi.z.zhang@linux.intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).