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Re: [PATCH] xfs: improve xfs_iext_destroy() by freeing extent indirectio

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH] xfs: improve xfs_iext_destroy() by freeing extent indirection array directly
From: Jeff Liu <jeff.liu@xxxxxxxxxx>
Date: Tue, 24 Sep 2013 22:05:20 +0800
Cc: "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20130923235017.GX9901@dastard>
References: <523C5E92.8000406@xxxxxxxxxx> <20130923003617.GM12541@dastard> <523FCA18.1000204@xxxxxxxxxx> <20130923235017.GX9901@dastard>
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:11.0) Gecko/20120410 Thunderbird/11.0.1
On 09/24/2013 07:50 AM, Dave Chinner wrote:

> On Mon, Sep 23, 2013 at 12:56:56PM +0800, Jeff Liu wrote:
>> On 09/23/2013 08:36 AM, Dave Chinner wrote:
>>
>>> On Fri, Sep 20, 2013 at 10:41:22PM +0800, Jeff Liu wrote:
>>>> From: Jie Liu <jeff.liu@xxxxxxxxxx>
>>>>
>>>> To free the incore file extents stores at the indirection array, we
>>>> call the common routine xfs_iext_irec_remove() to remove a record
>>>> from the array one at a time in reverse order, which will resize an
>>>> extent indirection array repeatedly according to the array size.
>>>>
>>>> This is not often the case to make a file with thousands extent records
>>>> stores at an indirection array, but above operation is inefficient and
>>>> could result in memory fragments.
>>>
>>> Yes, it may be inefficient, but I don't see that it's a contributor
>>> to memory fragmentation as the reallocated buffer is freed shortly
>>> after it has been allocated as the array shrinks. Do you have any
>>> evidence to suggest that such behaviour is actually fragmenting
>>> memory? If so, is the any test case that reproduces this problem?
>>
>> Ah, yes, it should not cause memory fragmentation.
>>
>> The benefits is that this change could save alloc/free buffers depending
>> on the number of extents records are stored at indirection array.
> 
> OK, can you send a new version with an updated commit message?

Sure, will post it soon.

Thanks,
-Jeff

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