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. -- Jens Axboe
