Matthew Wilcox <willy@xxxxxxxxxxxxx> writes: > 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! Ha! > 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? Thanks for the pointers, I can do it. - Alistair
