linux-kernel - Re: [PATCH 2/4] mm: cma: add functions to get region pages counters

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Message-id: <54E48FC3.5040902@partner.samsung.com>
Date:	Wed, 18 Feb 2015 16:12:35 +0300
From:	Safonov Dmitry <d.safonov@...tner.samsung.com>
To:	Gioh Kim <gioh.kim@....com>,
	Stefan Strogin <s.strogin@...tner.samsung.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	aneesh.kumar@...ux.vnet.ibm.com,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Pintu Kumar <pintu.k@...sung.com>,
	Weijie Yang <weijie.yang@...sung.com>,
	Laura Abbott <lauraa@...eaurora.org>,
	SeongJae Park <sj38.park@...il.com>,
	Hui Zhu <zhuhui@...omi.com>, Minchan Kim <minchan@...nel.org>,
	Dyasly Sergey <s.dyasly@...sung.com>,
	Vyacheslav Tyrtov <v.tyrtov@...sung.com>,
	gregory.0xf0@...il.com, sasha.levin@...cle.com, pavel@....cz,
	stefan.strogin@...il.com
Subject: Re: [PATCH 2/4] mm: cma: add functions to get region pages counters

Hello,
On 02/14/2015 10:32 AM, Gioh Kim wrote:
> 2015-02-13 오전 7:15에 Stefan Strogin 이(가) 쓴 글:
>> From: Dmitry Safonov <d.safonov@...tner.samsung.com>
>>
>> Here are two functions that provide interface to compute/get used size
>> and size of biggest free chunk in cma region.
> I usually just try to allocate memory, not check free size before try,
> becuase free size can be changed after I check it.
>
> Could you tell me why biggest free chunk size is necessary?
>
It may have changed after checking - at beginning of allocation
this information is completely useless as you mentioned, but
it may be very helpful after failed allocation to detect fragmentation
problem: i.e, you failed to alloc 20 Mb from 100 Mb CMA region
with 60 Mb free space, so you will know the reason.

-- 
Best regards,
Safonov Dmitry.

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