linux-nvdimm.lists.01.org archive mirror
 help / color / mirror / Atom feed
From: David Hildenbrand <david@redhat.com>
To: Mike Rapoport <rppt@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Andy Lutomirski <luto@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	Borislav Petkov <bp@alien8.de>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Christopher Lameter <cl@linux.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Elena Reshetova <elena.reshetova@intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
	James Bottomley <jejb@linux.ibm.com>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Matthew Wilcox <willy@infradead.org>,
	Matthew Garrett <mjg59@srcf.ucam.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Michal Hocko <mhocko@suse.com>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Michael Kerrisk <mtk.manpages@gmail.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Peter Zijlstra <peterz@infradead.org>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Rick Edgecombe <rick.p.edgecombe@intel.com>,
	Roman Gushchin <guro@fb.com>, Shakeel Butt <shakeelb@google.com>,
	S huah Khan <shuah@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Tycho Andersen <tycho@tycho.ws>, Will Deacon <will@kernel.org>,
	Yury Norov <yury.norov@gmail.com>,
	linux-api@vger.kernel.org, linux-arch@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
	linux-nvdimm@lists.01.org, linux-riscv@lists.infradead.org,
	x86@kernel.org, kernel test robot <oliver.sang@intel.com>
Subject: Re: [PATCH] secretmem: optimize page_is_secretmem()
Date: Mon, 19 Apr 2021 11:38:40 +0200	[thread overview]
Message-ID: <f4d0c4bf-423b-e227-444b-f1ea722dc43f@redhat.com> (raw)
In-Reply-To: <YH1PE4oWeicpJT9g@kernel.org>

On 19.04.21 11:36, Mike Rapoport wrote:
> On Mon, Apr 19, 2021 at 11:15:02AM +0200, David Hildenbrand wrote:
>> On 19.04.21 10:42, Mike Rapoport wrote:
>>> From: Mike Rapoport <rppt@linux.ibm.com>
>>>
>>> Kernel test robot reported -4.2% regression of will-it-scale.per_thread_ops
>>> due to commit "mm: introduce memfd_secret system call to create "secret"
>>> memory areas".
>>>
>>> The perf profile of the test indicated that the regression is caused by
>>> page_is_secretmem() called from gup_pte_range() (inlined by gup_pgd_range):
>>>
>>>    27.76  +2.5  30.23       perf-profile.children.cycles-pp.gup_pgd_range
>>>     0.00  +3.2   3.19 ± 2%  perf-profile.children.cycles-pp.page_mapping
>>>     0.00  +3.7   3.66 ± 2%  perf-profile.children.cycles-pp.page_is_secretmem
>>>
>>> Further analysis showed that the slow down happens because neither
>>> page_is_secretmem() nor page_mapping() are not inline and moreover,
>>> multiple page flags checks in page_mapping() involve calling
>>> compound_head() several times for the same page.
>>>
>>> Make page_is_secretmem() inline and replace page_mapping() with page flag
>>> checks that do not imply page-to-head conversion.
>>>
>>> Reported-by: kernel test robot <oliver.sang@intel.com>
>>> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
>>> ---
>>>
>>> @Andrew,
>>> The patch is vs v5.12-rc7-mmots-2021-04-15-16-28, I'd appreciate if it would
>>> be added as a fixup to the memfd_secret series.
>>>
>>>    include/linux/secretmem.h | 26 +++++++++++++++++++++++++-
>>>    mm/secretmem.c            | 12 +-----------
>>>    2 files changed, 26 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/include/linux/secretmem.h b/include/linux/secretmem.h
>>> index 907a6734059c..b842b38cbeb1 100644
>>> --- a/include/linux/secretmem.h
>>> +++ b/include/linux/secretmem.h
>>> @@ -4,8 +4,32 @@
>>>    #ifdef CONFIG_SECRETMEM
>>> +extern const struct address_space_operations secretmem_aops;
>>> +
>>> +static inline bool page_is_secretmem(struct page *page)
>>> +{
>>> +	struct address_space *mapping;
>>> +
>>> +	/*
>>> +	 * Using page_mapping() is quite slow because of the actual call
>>> +	 * instruction and repeated compound_head(page) inside the
>>> +	 * page_mapping() function.
>>> +	 * We know that secretmem pages are not compound and LRU so we can
>>> +	 * save a couple of cycles here.
>>> +	 */
>>> +	if (PageCompound(page) || !PageLRU(page))
>>> +		return false;
>>
>> I'd assume secretmem pages are rare in basically every setup out there. So
>> maybe throwing in a couple of likely()/unlikely() might make sense.
> 
> I'd say we could do unlikely(page_is_secretmem()) at call sites. Here I can
> hardly estimate which pages are going to be checked.
>   
>>> +
>>> +	mapping = (struct address_space *)
>>> +		((unsigned long)page->mapping & ~PAGE_MAPPING_FLAGS);
>>> +
>>
>> Not sure if open-coding page_mapping is really a good idea here -- or even
>> necessary after the fast path above is in place. Anyhow, just my 2 cents.
> 
> Well, most if the -4.2% of the performance regression kbuild reported were
> due to repeated compount_head(page) in page_mapping(). So the whole point
> of this patch is to avoid calling page_mapping().

I would have thought the fast path "(PageCompound(page) || 
!PageLRU(page))" would already avoid calling page_mapping() in many cases.


-- 
Thanks,

David / dhildenb
_______________________________________________
Linux-nvdimm mailing list -- linux-nvdimm@lists.01.org
To unsubscribe send an email to linux-nvdimm-leave@lists.01.org

  reply	other threads:[~2021-04-19  9:38 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-19  8:42 [PATCH] secretmem: optimize page_is_secretmem() Mike Rapoport
2021-04-19  9:15 ` David Hildenbrand
2021-04-19  9:36   ` Mike Rapoport
2021-04-19  9:38     ` David Hildenbrand [this message]
2021-04-19  9:40       ` David Hildenbrand
2021-04-19 10:14         ` Mike Rapoport
2021-04-19 10:21           ` David Hildenbrand
2021-04-19 11:43     ` Matthew Wilcox
2021-04-19 11:23 ` Matthew Wilcox
2021-04-19 11:56   ` Mike Rapoport
2021-04-19 12:21     ` Matthew Wilcox
2021-04-19 18:24       ` Mike Rapoport

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=f4d0c4bf-423b-e227-444b-f1ea722dc43f@redhat.com \
    --to=david@redhat.com \
    --cc=akpm@linux-foundation.org \
    --cc=arnd@arndb.de \
    --cc=bp@alien8.de \
    --cc=catalin.marinas@arm.com \
    --cc=cl@linux.com \
    --cc=dave.hansen@linux.intel.com \
    --cc=elena.reshetova@intel.com \
    --cc=guro@fb.com \
    --cc=hpa@zytor.com \
    --cc=jejb@linux.ibm.com \
    --cc=kirill@shutemov.name \
    --cc=linux-api@vger.kernel.org \
    --cc=linux-arch@vger.kernel.org \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-kselftest@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=linux-nvdimm@lists.01.org \
    --cc=linux-riscv@lists.infradead.org \
    --cc=luto@kernel.org \
    --cc=mark.rutland@arm.com \
    --cc=mhocko@suse.com \
    --cc=mingo@redhat.com \
    --cc=mjg59@srcf.ucam.org \
    --cc=mtk.manpages@gmail.com \
    --cc=oliver.sang@intel.com \
    --cc=palmer@dabbelt.com \
    --cc=paul.walmsley@sifive.com \
    --cc=peterz@infradead.org \
    --cc=rick.p.edgecombe@intel.com \
    --cc=rjw@rjwysocki.net \
    --cc=rppt@kernel.org \
    --cc=rppt@linux.ibm.com \
    --cc=shakeelb@google.com \
    --cc=shuah@kernel.org \
    --cc=tglx@linutronix.de \
    --cc=tycho@tycho.ws \
    --cc=viro@zeniv.linux.org.uk \
    --cc=will@kernel.org \
    --cc=willy@infradead.org \
    --cc=x86@kernel.org \
    --cc=yury.norov@gmail.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).