linux-ext4 - Re: [PATCH][RFC] ext4: avoid taking down_read(&grp->alloc

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Message-Id: <2D97EC87-86D8-41D9-8779-BB4A48E60E89@dilger.ca>
Date:	Mon, 14 Feb 2011 09:30:08 -0700
From:	Andreas Dilger <adilger@...ger.ca>
To:	"Amir G." <amir73il@...rs.sourceforge.net>
Cc:	Theodore Tso <tytso@....edu>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH][RFC] ext4: avoid taking down_read(&grp->alloc_sem)

On 2011-02-14, at 0:52, "Amir G." <amir73il@...rs.sourceforge.net> wrote:
>> @@ -1160,7 +1160,15 @@ ext4_mb_load_buddy(struct super_block *sb,
>> 
>> +       /*
>> +        * We only need to take the read lock if other groups share the buddy
>> +        * page with this group or if blocks may be added to this (last) group
>> +        * by ext4_group_extend().
>> +        */
>> +       if (blocks_per_page > 2 || group == sbi->s_groups_count - 1)
>> +               e4b->alloc_semp = &grp->alloc_sem;

No comment on whether this change is safe or not, but shouldn't this check be:

        if (blocks_per_page > 1 ||

Cheers, Andreas--
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