On Thu, Apr 4, 2024 at 7:45 PM Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
>
> On Fri, Apr 05, 2024 at 01:35:44AM +0000, Yosry Ahmed wrote:
> > Refactor limit and acceptance threshold checking outside of
> > zswap_store(). This code will be moved around in a following patch, so
> > it would be cleaner to move a function call around.
> >
> > Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
> > ---
> > mm/zswap.c | 32 ++++++++++++++++----------------
> > 1 file changed, 16 insertions(+), 16 deletions(-)
> >
> > diff --git a/mm/zswap.c b/mm/zswap.c
> > index 1cf3ab4b22e64..fba8f3c3596ab 100644
> > --- a/mm/zswap.c
> > +++ b/mm/zswap.c
> > @@ -1391,6 +1391,21 @@ static void zswap_fill_page(void *ptr, unsigned long value)
> > memset_l(page, value, PAGE_SIZE / sizeof(unsigned long));
> > }
> >
> > +static bool zswap_check_full(void)
> > +{
> > + unsigned long cur_pages = zswap_total_pages();
> > + unsigned long thr = zswap_accept_thr_pages();
>
> I know this looks neater, but it adds an extra division to the very
> common path where the limit hasn't been reached yet. It should really
> stay inside the branch.
I assumed the compiler is smart enough to do the division only when
necessary, but I didn't check tbh.
>
> Another option could be to precalculate the max and the accept
> threshold in absolute pages whenever their respective module param
> changes. That would eliminate both divisions from the hot path.
Yeah, that's better and cleaner. I will do that in the next version.
Thanks!
>
> > + unsigned long max_pages = zswap_max_pages();
> > +
> > + if (cur_pages >= max_pages) {
> > + zswap_pool_limit_hit++;
> > + zswap_pool_reached_full = true;
> > + } else if (zswap_pool_reached_full && cur_pages <= thr) {
> > + zswap_pool_reached_full = false;
> > + }
> > + return zswap_pool_reached_full;
> > +}
> > +
> > bool zswap_store(struct folio *folio)
> > {
> > swp_entry_t swp = folio->swap;
