linux-kernel - Re: [PATCH 2/4] mm: Create non-atomic version of SetPageReserved for init use

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Message-ID: <f4f6a343-7be1-4290-802e-7ff96e93bc2a@microsoft.com>
Date:   Wed, 12 Sep 2018 13:28:25 +0000
From:   Pasha Tatashin <Pavel.Tatashin@...rosoft.com>
To:     Alexander Duyck <alexander.duyck@...il.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
CC:     "mhocko@...e.com" <mhocko@...e.com>,
        "dave.jiang@...el.com" <dave.jiang@...el.com>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "dave.hansen@...el.com" <dave.hansen@...el.com>,
        "jglisse@...hat.com" <jglisse@...hat.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "logang@...tatee.com" <logang@...tatee.com>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH 2/4] mm: Create non-atomic version of SetPageReserved for
 init use


On 9/10/18 7:43 PM, Alexander Duyck wrote:
> From: Alexander Duyck <alexander.h.duyck@...el.com>
> 
> It doesn't make much sense to use the atomic SetPageReserved at init time
> when we are using memset to clear the memory and manipulating the page
> flags via simple "&=" and "|=" operations in __init_single_page.
> 
> This patch adds a non-atomic version __SetPageReserved that can be used
> during page init and shows about a 10% improvement in initialization times
> on the systems I have available for testing. On those systems I saw
> initialization times drop from around 35 seconds to around 32 seconds to
> initialize a 3TB block of persistent memory.
> 
> I tried adding a bit of documentation based on commit <f1dd2cd13c4> ("mm,
> memory_hotplug: do not associate hotadded memory to zones until online").
> 
> Ideally the reserved flag should be set earlier since there is a brief
> window where the page is initialization via __init_single_page and we have
> not set the PG_Reserved flag. I'm leaving that for a future patch set as
> that will require a more significant refactor.
> 
> Acked-by: Michal Hocko <mhocko@...e.com>
> Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>

Reviewed-by: Pavel Tatashin <pavel.tatashin@...rosoft.com>

Thank you,
Pavel