linux-kernel - Re: [v4 4/6] mm/memory_hotplug: optimize probe routine

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Message-ID: <20180216091304.hgp5tn25nleuy4jc@gmail.com>
Date:   Fri, 16 Feb 2018 10:13:04 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>
Cc:     steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        akpm@...ux-foundation.org, mgorman@...hsingularity.net,
        mhocko@...e.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        gregkh@...uxfoundation.org, vbabka@...e.cz,
        bharata@...ux.vnet.ibm.com, tglx@...utronix.de, mingo@...hat.com,
        hpa@...or.com, x86@...nel.org, dan.j.williams@...el.com,
        kirill.shutemov@...ux.intel.com, bhe@...hat.com
Subject: Re: [v4 4/6] mm/memory_hotplug: optimize probe routine


* Pavel Tatashin <pasha.tatashin@...cle.com> wrote:

> When memory is hotplugged pages_correctly_reserved() is called to verify
> that the added memory is present, this routine traverses through every
> struct page and verifies that PageReserved() is set. This is a slow
> operation especially if a large amount of memory is added.
> 
> Instead of checking every page, it is enough to simply check that the
> section is present, has mapping (struct page array is allocated), and the
> mapping is online.
> 
> In addition, we should not excpect that probe routine sets flags in struct
> page, as the struct pages have not yet been initialized. The initialization
> should be done in __init_single_page(), the same as during boot.
> 
> Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>

Reviewed-by: Ingo Molnar <mingo@...nel.org>

Thanks,

	Ingo