linux-kernel - Re: [PATCH] mm, kmemleak: Little optimization while scanning

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Date:   Fri, 7 Dec 2018 09:48:19 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm, kmemleak: Little optimization while scanning

On Thu, Dec 06, 2018 at 02:19:18PM +0100, Oscar Salvador wrote:
> kmemleak_scan() goes through all online nodes and tries
> to scan all used pages.
> We can do better and use pfn_to_online_page(), so in case we have
> CONFIG_MEMORY_HOTPLUG, offlined pages will be skiped automatically.
> For boxes where CONFIG_MEMORY_HOTPLUG is not present, pfn_to_online_page()
> will fallback to pfn_valid().
> 
> Another little optimization is to check if the page belongs to the node
> we are currently checking, so in case we have nodes interleaved we will
> not check the same pfn multiple times.
> 
> I ran some tests:
> 
> Add some memory to node1 and node2 making it interleaved:
> 
> (qemu) object_add memory-backend-ram,id=ram0,size=1G
> (qemu) device_add pc-dimm,id=dimm0,memdev=ram0,node=1
> (qemu) object_add memory-backend-ram,id=ram1,size=1G
> (qemu) device_add pc-dimm,id=dimm1,memdev=ram1,node=2
> (qemu) object_add memory-backend-ram,id=ram2,size=1G
> (qemu) device_add pc-dimm,id=dimm2,memdev=ram2,node=1
> 
> Then, we offline that memory:
>  # for i in {32..39} ; do echo "offline" > /sys/devices/system/node/node1/memory$i/state;done
>  # for i in {48..55} ; do echo "offline" > /sys/devices/system/node/node1/memory$i/state;don
>  # for i in {40..47} ; do echo "offline" > /sys/devices/system/node/node2/memory$i/state;done
> 
> And we run kmemleak_scan:
> 
>  # echo "scan" > /sys/kernel/debug/kmemleak
> 
> before the patch:
> 
> kmemleak: time spend: 41596 us
> 
> after the patch:
> 
> kmemleak: time spend: 34899 us
> 
> Signed-off-by: Oscar Salvador <osalvador@...e.de>

Acked-by: Catalin Marinas <catalin.marinas@....com>