[Ocfs2-devel] [PATCH 2/3] Ocfs2: Add a new code 'OCFS2_INFO_FREEINODE' for o2info ioctl.

[Tristan Ye <tristan.ye@oracle.com>]

Joel Becker wrote:
> On Tue, Feb 22, 2011 at 04:02:15PM +0800, Tristan Ye wrote:
>>     Thanks for putting forward the point. I'm afraid that I'm not an 
>> enough experienced
>> user to talk issues on 'GFP_NOFS VS GFP_KERNEL' too much;-)
>>    
>>     Per my understanding, can the GFP_NOFS become a real overkill when 
>> claiming around 2k memory?
>> Having known that GFP_NOFS is more restrictive and more secure to 
>> filesystem code for avoiding potential
>> deadlock, do we really need to use GFP_KERNEL instead of GFP_NOFS there?
>
> 	In general, we should use the least restrictive mode that is
> safe.  GFP_KERNEL tries the hardest to get memory, and it sleeps the
> most, but it therefore gives the user the fewest ENOMEMs.
>
>>     Btw, is there a explicit rule/convention on when to use GFP_NOFS or 
>> GFP_KERNEL? e.g:
>
> 	One uses GFP_NOFS when filesystem writeback cannot be used to
> free memory.  So if you're in the ocfs2 writeback code, you can't have
> an allocation try to start writeback ;-)  That's why you use GFP_NOFS.
> 	When you are holding no locks, and blocking nothing related to
> writeout, there is no reason to limit yourself.

    Loved your explanation, it makes great sense to me;-)


>
> Joel
>