linux-kernel - Re: [PATCH v2 3/4] fat: mark superblock as dirty less often

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Date:	Sat, 14 Apr 2012 19:37:56 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	dedekind1@...il.com
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Maling List <linux-kernel@...r.kernel.org>,
	Linux FS Maling List <linux-fsdevel@...r.kernel.org>,
	Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>
Subject: Re: [PATCH v2 3/4] fat: mark superblock as dirty less often

Artem Bityutskiy <dedekind1@...il.com> writes:

> On Sat, 2012-04-14 at 18:17 +0900, OGAWA Hirofumi wrote:
>> Artem Bityutskiy <dedekind1@...il.com> writes:
>> 
>> > From: Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>
>> >
>> > This patch is a preparation for further changes. It touches few functions
>> > in fatent.c and prevents them from marking the superblock as dirty
>> > unnecessarily often. Namely, instead of marking it as dirty in the internal
>> > tight loops - do it only once at the end of the functions. And instead of
>> > marking it as dirty while holding the FAT table lock, do it
>> > outside the lock.
>> >
>> > The reason for this patch is that marking the superblock as dirty will soon
>> > become a little bit heavier operation, so it is cleaner to do this
>> > only when it
>> > is necessary.
>> 
>> For it, please use local variable like,
>> 
>> 
>> {
>>        	int fsinfo_dirty = 0;
>> 
>> 	while (1) {
>>         	change free_clusters
>>                 fsinfo_dirty = 1;
>>         }
>> 
>>         if (fsinfo_dirty)
>>         	mark_fsinfo_dirty()
>> }
>> 
>> instead of dirty it always.
>
> But could you please explain why do we need an extra variable? What is
> the problem with doing all our FAT table changes and then marking the
> FSINFO as dirty?

Above example may not be proper. I meant please dirty FSINFO only if
necessary. Your patch seems to be dirty even if code didn't change
FSINFO.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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