Re: [fuse-devel] [fuse] Speeding up readdir()

[Nikolaus Rath <Nikolaus@rath.org>]

On Dec 07 2018, Miklos Szeredi <miklos@szeredi.hu> wrote:
> On Thu, Dec 6, 2018 at 9:01 PM Nikolaus Rath <Nikolaus@rath.org> wrote:
>>
>> Hello,
>>
>> I am trying to improve the performance of readdir() requests. I have a
>> client application that issues a lot of readdir() requests, and a FUSE
>> filesystem that makes extensive use of kernel caching for inode entry
>> attributes because retrieving the attributes from the backend is
>> relatively expensive.
>>
>> Unfortunately, it seems to me that currently there is no way to avoid
>> having to retrieve the attributes from the backend for every entry that
>> is returned by readdir - on every call:
>>
>> If I am using readdirplus, I have to include the full attributes even if
>> the kernel already has them cached.
>>
>> If I disable readdirplus, I can return just the entry name and its inode
>> - but I believe because this doesn't result in a lookup count increase
>> of the inode, the kernel can't match this with the existing cached data
>> for the inode (is that correct?) and I'm getting a separate lookup()
>> request for each entry that I've returned.
>
> Was the entry timed out?  If not, then there shouldn't've been a
> lookup.

I am not 100% sure because of the atime invalidation issue. Apart from
that, it definitely was not timed out.

Are you saying that I should not be seeing lookup() requests after
(non-plus) readdir() if the dentry is already cached?

Best,
-Nikolaus

-- 
GPG Fingerprint: ED31 791B 2C5C 1613 AF38 8B8A D113 FCAC 3C4E 599F

             »Time flies like an arrow, fruit flies like a Banana.«