On Fri, 2022-04-01 at 14:53 +1100, Dave Chinner wrote: > On Thu, Mar 31, 2022 at 06:56:32PM -0400, Jeff Layton wrote: > > The inode_insert5 currently looks at I_CREATING to decide whether to > > insert the inode into the sb list. This test is a bit ambiguous though > > as I_CREATING state is not directly related to that list. > > > > This test is also problematic for some upcoming ceph changes to add > > fscrypt support. We need to be able to allocate an inode using new_inode > > and insert it into the hash later if we end up using it, and doing that > > now means that we double add it and corrupt the list. > > > > What we really want to know in this test is whether the inode is already > > in its superblock list, and then add it if it isn't. Have it test for > > list_empty instead and ensure that we always initialize the list by > > doing it in inode_init_once. It's only ever removed from the list with > > list_del_init, so that should be sufficient. > > > > Suggested-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> > > --- > > fs/inode.c | 11 ++++++++--- > > 1 file changed, 8 insertions(+), 3 deletions(-) > > > > This is the alternate approach that Al suggested to me on IRC. I think > > this is likely to be more robust in the long run, and we can avoid > > exporting another symbol. > > Looks good to me. > > Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx> > > FWIW, I'm getting ready to resend patches originally written by > Waiman Long years ago to convert the inode sb list to a different > structure (per-cpu lists) for scalability reasons, but is still > allows using list-empty() to check if the inode is on the list or > not so I dont' see a problem with this change at all. > Thanks, Dave. > > Al, if you're ok with this, would you mind taking this in via your tree? > > I'd like to see this in sit in linux-next for a bit so we can see if any > > benchmarks get dinged. > > I think that is unlikely - the sb inode list just doesn't show up in > profiles until you are pushing several hundred thousand inodes a > second through the inode cache and there really aren't a lot of > worklaods out there that do that. At that point, sb list lock > contention becomes the issue, not the requirement to add in-use > inodes to the sb list... > My (minor) concern was that since we're now initializing this list for all allocations, not just in new_inode, it could potentially slow down some callers. I agree that it seems pretty unlikely to be an issue though. > e.g. concurrent 'find <...> -ctime' operations on XFS hit sb list > lock contention limits at about 600,000 inodes/s being, > instantiated, stat()d and reclaimed from memory. With > Waiman's dlist code I mention above, it'll do 1.5 million inodes/s > for the same CPU usage. And a concurrent bulkstat workload goes > from 600,000 inodes/s to over 6 million inodes/s for the same > CPU usage. That bulkstat workload is hitting memory reclaim > scalability limits as I'm turning over ~12GB/s of cached memory on a > machine with only 16GB RAM... > > Cheers, > > Dave. -- Jeff Layton <jlayton@xxxxxxxxxx>
