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
And I cannot find where any of these counters are documents, so I cannot
say what is "correct".
Well.... arch/s390/appldata/appldata_mem.c says
u64 pswpin; /* pages swapped in */
u64 pswpout; /* pages swapped out */
but that isn't exactly unambiguous, and is for s390 which doesn't
support THP_SWAP
Ho hum. I guess I put that back as it was.
Thanks for the review!!!
NeilBrown
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.