Re: [PATCH 2/2] Btrfs: load the key from the dir item in readdir into a fake dentry

[Josef Bacik <josef@redhat.com>]

On 05/26/2011 04:03 PM, Andi Kleen wrote:
> On Thu, May 26, 2011 at 03:02:42PM -0400, Josef Bacik wrote:
>> +	/*
>> +	 * If this dentry needs lookup, don't set the referenced flag so that it
>> +	 * is more likely to be cleaned up by the dcache shrinker in case of
>> +	 * memory pressure.
>> +	 */
>> +	if (!d_need_lookup(dentry))
>> +		dentry->d_flags |= DCACHE_REFERENCED;
> 
> No it doesn't at all. The allocation will just push everything else
> out.
> 
> Really you cannot view this by only looking at the dcache.
> You have to look at the complete VM behaviour. All the caches
> and the other memory interact.

Agreed, but this makes it monumentally easier to push these entries out
of the cache, which is the best I can do with what I have for now.

>>
>>
>>> d_alloc uses a normal GFP_KERNEL, which is quite in appropiate for this.
>>>
>>> It should at least reclaim and probably more, but even then it's
>>> risky.
>>>
>>
>> Ah yeah I guess I should have probably used GFP_KERNEL.  Sorry about that,
> 
> GFP_KERNEL is already used, but it's wrong. I'm not sure any
> of the existing GFP_* flags will give you the semantics you
> need in fact. The new flag Minchan added for readahead may come
> near, but even that is probably not enough.

Yeah if there was a GFP_DONTTRYTOHARD I would use that but there isn't.
 Maybe I'll code that up.  Thanks,

Josef