On Sun, Jul 11, 2021 at 07:44:07PM -0600, Jens Axboe wrote: > On 7/11/21 9:09 AM, Matthew Wilcox (Oracle) wrote: > > I noticed a theoretical case where an IOCB_NOWAIT read could sleep: > > > > filemap_get_pages > > filemap_get_read_batch > > page_cache_sync_readahead > > page_cache_sync_ra > > ondemand_readahead > > do_page_cache_ra > > page_cache_ra_unbounded > > gfp_t gfp_mask = readahead_gfp_mask(mapping); > > memalloc_nofs_save() > > __page_cache_alloc(gfp_mask); > > > > We're in a nofs context, so we're not going to start new IO, but we might > > wait for writeback to complete. We generally don't want to sleep for IO, > > particularly not for IO that isn't related to us. > > > > Jens, can you run this through your test rig and see if it makes any > > practical difference? > > You bet, I'll see if I can trigger this condition and verify we're no > longer blocking on writeback. Thanks for hacking this up. Did you have any success yet?
