On Mon, May 02, 2022 at 03:28:49PM +1000, NeilBrown wrote: > On Mon, 02 May 2022, Matthew Wilcox wrote: > > On Mon, May 02, 2022 at 02:57:46PM +1000, NeilBrown wrote: > > > @@ -390,9 +392,9 @@ static void sio_read_complete(struct kiocb *iocb, long ret) > > > struct page *page = sio->bvec[p].bv_page; > > > > > > SetPageUptodate(page); > > > + count_swpout_vm_event(page); > > > unlock_page(page); > > > } > > > - count_vm_events(PSWPIN, sio->pages); > > > > Surely that should be count_swpIN_vm_event? > > > I'm not having a good day.... > > Certainly shouldn't be swpout. There isn't a count_swpin_vm_event(). > > swap_readpage() only counts once for each page no matter how big it is. > While swap_writepage() counts one for each PAGE_SIZE written. > > And we have THP_SWPOUT but not THP_SWPIN _If_ I understand the swap-in patch correctly (at least as invoked by shmem), it won't attempt to swap in an entire THP. Even if it swapped out an order-9 page, it will bring in order-0 pages from swap, and then rely on khugepaged to reassemble them. Someone who actually understands the swap code should check that my explanation here is correct.
