Hi Miklos, [ adding Laura to CC, something I should have done before ] On Mon, Mar 10 2025, Miklos Szeredi wrote: > On Fri, 7 Mar 2025 at 16:31, Luis Henriques <luis@xxxxxxxxxx> wrote: > >> Any further feedback on this patch, or is it already OK for being merged? > > The patch looks okay. I have ideas about improving the name, but that can wait. > > What I think is still needed is an actual use case with performance numbers. As requested, I've run some tests on CVMFS using this kernel patch[1]. For reference, I'm also sharing the changes I've done to libfuse[2] and CVMFS[3] in order to use this new FUSE operation. The changes to these two repositories are in a branch named 'wip-notify-inc-epoch'. As for the details, basically what I've done was to hack the CVMFS loop in FuseInvalidator::MainInvalidator() so that it would do a single call to the libfuse operation fuse_lowlevel_notify_increment_epoch() instead of cycling through the inodes list. The CVMFS patch is ugly, it just short-circuiting the loop, but I didn't want to spend any more time with it at this stage. The real patch will be slightly more complex in order to deal with both approaches, in case the NOTIFY_INC_EPOCH isn't available. Anyway, my test environment was a small VM, where I have two scenarios: a small file-system with just a few inodes, and a larger one with around 8000 inodes. The test approach was to simply mount the filesystem, load the caches with 'find /mnt' and force a flush using the cvmfs_swissknife tool, with the 'ingest' command. [ Disclosure: my test environment actually uses a fork of upstream cvmfs, but for the purposes of these tests that shouldn't really make any difference. ] The numbers in the table below represent the average time (tests were run 100 times) it takes to run the MainInvalidator() function. As expected, using the NOTIFY_INC_EPOCH is much faster, as it's a single operation, a single call into FUSE. Using the NOTIFY_INVAL_* is much more expensive -- it requires calling into the kernel several times, depending on the number of inodes on the list. |------------------+------------------+----------------| | | small filesystem | "big" fs | | | (~20 inodes) | (~8000 inodes) | |------------------+------------------+----------------| | NOTIFY_INVAL_* | 330 us | 4300 us | | NOTIFY_INC_EPOCH | 40 us | 45 us | |------------------+------------------+----------------| Hopefully these results help answering Miklos questions regarding the cvmfs use-case. [1] https://lore.kernel.org/all/20250226091451.11899-1-luis@xxxxxxxxxx/ [2] https://github.com/luis-henrix/libfuse [3] https://github.com/luis-henrix/cvmfs Cheers, -- Luís
