> >> > > > > So we always had a fallback to do_page_cache_ra() if the size of the > > readahead is less than 4 pages (16k). I think this was there because we > > were adding `2` to the new_order: > > If this is the reason for the magic number 4, then it's a bug in itself IMHO. 4 > pages is only 16K when the page size is 4K; arm64 supports other page sizes. But > additionally, it's not just ra->size that dictates the final order of the folio; > it also depends on alignment in the file, EOF, etc. > IIRC, initially we were not able to use order-1 folios[1], so we always did a fallback for any order < 2 using do_page_cache_ra(). I think that is where the magic order 2 (4 pages) is coming. Please someone can correct me if I am wrong. But we don't have that limitation for file-backed folios anymore, so the fallback for ra->size < 4 is probably not needed. So the only time we do a fallback is if we don't support large folios. > If we remove the fallback condition completely, things will still work out. So > unless someone can explain the reason for that condition (Matthew?), my vote > would be to remove it entirely. I am actually fine with removing the first part of this fallback condition. But as I said, we still need to do a fallback if we don't support large folios. -- Pankaj [1] https://lore.kernel.org/all/ZH0GvxAdw1RO2Shr@xxxxxxxxxxxxxxxxxxxx/
