linux-kernel - Re: [PATCH/RFC] mm: add and use batched version of __tlb_remove

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Message-ID: <22a7534c-4759-4e7e-de07-d33a3682c156@virtuozzo.com>
Date:   Thu, 23 Dec 2021 12:55:38 +0300
From:   Nikita Yushchenko <nikita.yushchenko@...tuozzo.com>
To:     Dave Hansen <dave.hansen@...el.com>, Will Deacon <will@...nel.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nick Piggin <npiggin@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        sparclinux@...r.kernel.org, kernel@...nvz.org
Subject: Re: [PATCH/RFC] mm: add and use batched version of
 __tlb_remove_table()

>> I currently don't have numbers for this patch taken alone. This patch
>> originates from work done some years ago to reduce cost of memory
>> accounting, and x86-only version of this patch was in virtuozzo/openvz
>> kernel since then. Other patches from that work have been upstreamed,
>> but this one was missed.
>>
>> Still it's obvious that release_pages() shall be faster that a loop
>> calling put_page() - isn't that exactly the reason why release_pages()
>> exists and is different from a loop calling put_page()?
> 
> Yep, but this patch does a bunch of stuff to some really hot paths.  It
> would be greatly appreciated if you could put in the effort to actually
> put some numbers behind this.  Plenty of weird stuff happens on
> computers that we suck at predicting.

I found the original report about high cost of memory accounting, and tried to repeat the test described 
there, with and without the patch.

The test is - run a script in 30 openvz containers in parallel, and measure average time per execution. 
Script is attached.

I'm getting measurable improvement in average msecs per execution: 15360 ms without patch, 15170 ms with 
patch. And this difference is reliably reproducible.

Nikita

Download attachment "calcprimes.sh" of type "application/x-sh" (469 bytes)