problem with cache size

[Maxim Dounin]

Hello!

On Fri, Mar 01, 2013 at 05:41:18PM +0200, Anatoli Marinov wrote:

> Hi,
> I have a strange problem with cache size on XFS. I tried to debug it and I
> found something.
> 
> First there is a test request for 1 file which is 10 MB.
> In the function ngx_http_file_cache_update I have counted size 17039360
> because st_blocks = 33280,  st_size = 10486040.
> 
> After that I am trying to restart the server and cache manager add this
> size for cache structure but the size is different as follow
> for cache size the increment is with 10489856,  st_size = 10486040,
> st_blocks = 20488
> 
> As could be seen st_blocks is different for one and the same file.
> I think the second file size is right but why the first is wrong?

This is an known XFS feature, it reports preallocated blocks 
instead of a real size before the file is closed.  Some details 
are here:

http://trac.nginx.org/nginx/ticket/157

-- 
Maxim Dounin
http://nginx.org/en/donation.html