On Mon, Apr 11, 2022 at 10:10:23AM +0800, JeffleXu wrote: > > > On 4/8/22 8:06 PM, Vivek Goyal wrote: > > On Fri, Apr 08, 2022 at 07:50:55PM +0800, JeffleXu wrote: > >> > >> > >> On 4/8/22 7:25 PM, Vivek Goyal wrote: > >>> On Fri, Apr 08, 2022 at 10:36:40AM +0800, JeffleXu wrote: > >>>> > >>>> > >>>> On 4/7/22 10:10 PM, Vivek Goyal wrote: > >>>>> On Sat, Apr 02, 2022 at 06:32:50PM +0800, Jeffle Xu wrote: > >>>>>> Move dmap free worker kicker inside the critical region, so that extra > >>>>>> spinlock lock/unlock could be avoided. > >>>>>> > >>>>>> Suggested-by: Liu Jiang <gerry@xxxxxxxxxxxxxxxxx> > >>>>>> Signed-off-by: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx> > >>>>> > >>>>> Looks good to me. Have you done any testing to make sure nothing is > >>>>> broken. > >>>> > >>>> xfstests -g quick shows no regression. The tested virtiofs is mounted > >>>> with "dax=always". > >>> > >>> I think xfstests might not trigger reclaim. You probably will have to > >>> run something like blogbench with a small dax window like 1G so that > >>> heavy reclaim happens. > >> > >> > >> Actually, I configured the DAX window to 8MB, i.e. 4 slots when running > >> xfstests. Thus I think the reclaim path is most likely triggered. > >> > >> > >>> > >>> For fun, I sometimes used to run it with a window of just say 16 dax > >>> ranges so that reclaim was so heavy that if there was a bug, it will > >>> show up. > >>> > >> > >> Yeah, my colleague had ever reported that a DAX window of 4KB will cause > >> hang in our internal OS (which is 4.19, we back ported virtiofs to > >> 4.19). But then I found that this issue doesn't exist in the latest > >> upstream. The reason seems that in the upstream kernel, > >> devm_memremap_pages() called in virtio_fs_setup_dax() will fail directly > >> since the dax window (4KB) is not aligned with the sparse memory section. > > > > Given our default chunk size is 2MB (FUSE_DAX_SHIFT), may be it is not > > a bad idea to enforce some minimum cache window size. IIRC, even one > > range is not enough. Minimum 2 are required for reclaim to not deadlock. > > Curiously, why minimum 1 range is not adequate? In which case minimum 2 > are required? Frankly speaking, right now I don't remember. I have vague memories of concluding in the past that 1 range is not sufficient. But if you like dive deeper, and try with one range and see if you can introduce deadlock. Thanks Vivek
