Re: [PATCH 1/3]fs/inode: iunique() Optimize Performance

[liu weni <qingshenlwy@gmail.com>]

Thanks, I will try others way to improve the performance.


2009/11/26 Matthew Wilcox <matthew@wil.cx>:
> On Wed, Nov 25, 2009 at 08:20:02PM +0100, J?r?my Cochoy wrote:
>> Hello,
>>
>> There is something strange in iunique : what will happend if all inode
>> between max_reserved+1 and (unsinged in)(0-1) ? Will it make an
>> infinite loop or an interruption can happen and make an inode become
>> free?
>
> Another process can free an inode while this loop is executing.
>
>> In that case, it will be better to stop search when counter overflow, no?
>
> If you have all four billion inodes allocated, you have significantly
> bigger problems than this loop.  For a start, at 600 bytes per inode,
> I'd like to see your machine with 2.4TB of memory.  Then there's the
> size of your inode hash, and the depth of the chains within it.
>
>> Will it not be better to use a field max_ino_used (in superblock, for
>> exemple) where we store the last inode allocated with iunique and make
>> a search only if max_ino_used become to (unsigned)(-1) ?
>>
>> But, if iunique is here to provide a solution in order to generate
>> unused inode in filesystem which have various inode number, it's
>> better to use a list of used ino, in a short hash table which use the
>> first 8 bits of the inode, always use the same function to create a
>> new inode and look at the head if we can add a new inode with bigger
>> ino and still in the range. (But i think filesystems developper prefer
>> to write ther own functions in order to do that, no?)
>>
>> Well, if we want to stop in case of full inode filesystem, we can put
>> the first condition in the head and add change return as :
>> return inode->i_ino > max_reserved ? res : 0; // 0 might "i can't find
>> an inode after max_reserved"
>
> Gloves.
>
> http://thedailywtf.com/Articles/The_Complicator_0x27_s_Gloves.aspx
>
> --
> Matthew Wilcox                          Intel Open Source Technology Centre
> "Bill, look, we understand that you're interested in selling us this
> operating system, but compare it to ours.  We can't possibly take such
> a retrograde step."
>
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