On Fri, Jun 03, 2022 at 05:12:33PM +1000, Alistair Popple wrote: > +++ b/mm/filemap.c > @@ -3168,8 +3168,9 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) > VM_BUG_ON_FOLIO(!folio_contains(folio, index), folio); > > /* > - * We have a locked page in the page cache, now we need to check > - * that it's up-to-date. If not, it is going to be due to an error. > + * We have a locked page in the page cache. Check that it's up-to-date. > + * If not it is because there was no page in the page cache (only likely > + * in the case of MADV_RANDOM) or due to error. The comment is correct, but the code is buggy! We should be calling page_cache_ra_order() in do_sync_mmap_readahead(), even if VM_RAND_READ is set (or !ra_pages, or mmap_miss is high). At least for one page. That would allow us to drop the FGP_FOR_MMAP flag as page_cache_ra_order() will instantiate a folio for us. Do you want to write that patch or should I do it?
