linux-ext4 - Re: [RFC][PATCH 1/7]ext4: Add EXT4_IOC_ADD_GLOBAL_ALLOC

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Message-ID: <20090627165400.GA9414@skywalker>
Date:	Sat, 27 Jun 2009 22:24:00 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Greg Freemyer <greg.freemyer@...il.com>
Cc:	Andreas Dilger <adilger@....com>,
	Akira Fujita <a-fujita@...jp.nec.com>,
	linux-ext4@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>,
	linux-fsdevel@...r.kernel.org,
	Aneesh Kumar <aneesh.kumar@...il.com>
Subject: Re: [RFC][PATCH 1/7]ext4: Add EXT4_IOC_ADD_GLOBAL_ALLOC_RULE
	restricts block allocation

On Thu, Jun 25, 2009 at 08:47:59AM -0400, Greg Freemyer wrote:
> Aneesh,
> 
> Can you provide the below requested info?
> 
> Thanks
> Greg
> 
> On Tue, Jun 23, 2009 at 8:11 PM, Andreas Dilger<adilger@....com> wrote:
> > On Jun 23, 2009  20:02 -0400, Greg Freemyer wrote:
> >> On Tue, Jun 23, 2009 at 7:19 PM, Andreas Dilger<adilger@....com> wrote:
> >> > On Jun 23, 2009  17:25 +0900, Akira Fujita wrote:
> >> >> alloc_flag of ext4_alloc_rule structure is set as "mandatory" or "advisory".
> >> >> Restricted blocks with "mandatory" are never used by block allocator.
> >> >> But in "advisory" case, block allocator is allowed to use restricted blocks
> >> >> when there are no free blocks on FS.
> >> >
> >> > Would it make more sense to implement the range protections via the
> >> > existing preallocation ranges (PA)?  An inode can have multiple
> >> > PAs attached to it to have it prefer allocations from that range.
> >> >
> >> > We could also attach PAs to the superblock to prevent other files from
> >> > allocating out of those ranges.  This would work better with the existing
> >> > allocation code instead of creating a second similar mechanism.
> >>
> >> Where can I find documentation about how PA works?  Or is it just in
> >> the source?  If so, what are one or two calls that cause the PA ranges
> >> to be set, etc.
> >

Mostly the source. Some of mballoc details are documented in the ols
2008 paper. Regarding some of the functions

ext4_mb_use_preallocated -> allocate from PA
ext4_mb_new_preallocation -> Create new PA.

Source code also have some documentation that explains how mballoc use
PA.

-aneesh
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