linux-kernel - Re: [mm PATCH v5 6/7] mm: Add reserved flag setting to set_page

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Message-ID: <20181110021105.ln7geexvln5ap5fg@xakep.localdomain>
Date:   Fri, 9 Nov 2018 21:11:05 -0500
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvdimm@...ts.01.org, davem@...emloft.net,
        pavel.tatashin@...rosoft.com, mhocko@...e.com, mingo@...nel.org,
        kirill.shutemov@...ux.intel.com, dan.j.williams@...el.com,
        dave.jiang@...el.com, rppt@...ux.vnet.ibm.com, willy@...radead.org,
        vbabka@...e.cz, khalid.aziz@...cle.com, ldufour@...ux.vnet.ibm.com,
        mgorman@...hsingularity.net, yi.z.zhang@...ux.intel.com
Subject: Re: [mm PATCH v5 6/7] mm: Add reserved flag setting to set_page_links

On 18-11-05 13:19:56, Alexander Duyck wrote:
> This patch modifies the set_page_links function to include the setting of
> the reserved flag via a simple AND and OR operation. The motivation for
> this is the fact that the existing __set_bit call still seems to have
> effects on performance as replacing the call with the AND and OR can reduce
> initialization time.
> 
> Looking over the assembly code before and after the change the main
> difference between the two is that the reserved bit is stored in a value
> that is generated outside of the main initialization loop and is then
> written with the other flags field values in one write to the page->flags
> value. Previously the generated value was written and then then a btsq
> instruction was issued.
> 
> On my x86_64 test system with 3TB of persistent memory per node I saw the
> persistent memory initialization time on average drop from 23.49s to
> 19.12s per node.
> 
> Signed-off-by: Alexander Duyck <alexander.h.duyck@...ux.intel.com>

Reviewed-by: Pavel Tatashin <pasha.tatashin@...een.com>