On Fri, 15 May 2015 15:15:48 -0600 Andreas Dilger <adil...@dilger.ca> wrote:
> On May 14, 2015, at 5:23 AM, Dave Chinner <da...@fromorbit.com> wrote: > > > > On Wed, May 13, 2015 at 08:52:59PM -0700, Linus Torvalds wrote: > >> On Wed, May 13, 2015 at 8:30 PM, Al Viro <v...@zeniv.linux.org.uk> wrote: > >>> > >>> Maybe... I'd like to see the profiles, TBH - especially getxattr() and > >>> access() frequency on various loads. Sure, make(1) and cc(1) really care > >>> about stat() very much, but I wouldn't be surprised if something like > >>> httpd or samba would be hitting getxattr() a lot... > >> > >> So I haven't seen samba profiles in ages, but iirc we have more > >> serious problems than trying to speed up basic filename lookup. > >> > >> At least long long ago, inode semaphore contention was a big deal, > >> largely due to readdir(). > > > > It still is - it's the prime reason people still need to create > > hashed directory structures so that they can get concurrency in > > directory operations. IMO, concurrency in directory operations is a > > more important problem to solve than worrying about readdir speed; > > in large filesystems readdir and lookup are IO bound operations and > > so everything serialises on the IO as it's done with the i_mutex > > held.... > > We've had a patch[*] to add ext4 parallel directory operations in Lustre for > a few years, that adds separate locks for each internal tree and leaf block > instead of using i_mutex, so it scales as the size of the directory grows. > This definitely improved many-threaded directory create/lookup/unlink > performance (rename still uses a single lock). .. and I've been wondering what to do about i_mutex and NFS. I've had customer reports of slowness in creating files that seems to be due to i_mutex on the directory being held over the whole 'create' RPC, so only one of those can be in flight at the one time. "make -j" on a large source directory can easily want to create lots of "*.o" files at "the same time". And NFS doesn't need i_mutex at all because the server will provide the needed guarantees. NeilBrown
pgpWsIZ4vWP5d.pgp
Description: OpenPGP digital signature
