On Wed, Jul 15, 2015 at 12:42:28PM -0700, Andres Lagar-Cavilla wrote:
> On Wed, Jul 15, 2015 at 6:54 AM, Vladimir Davydov
> <[email protected]> wrote:
[...]
> > +static void kpageidle_clear_pte_refs(struct page *page)
> > +{
> > + struct rmap_walk_control rwc = {
> > + .rmap_one = kpageidle_clear_pte_refs_one,
> > + .anon_lock = page_lock_anon_vma_read,
> > + };
> > + bool need_lock;
> > +
> > + if (!page_mapped(page) ||
>
> Question: what about mlocked pages? Is there any point in calculating
> their idleness?
Those can be filtered out with the aid of /proc/kpageflags (this is what
the script attached to patch #0 of the series actually does). We have to
read the latter anyway in order to get information about THP. That said,
I prefer not to introduce any artificial checks for locked memory. Who
knows, may be one day somebody will use this API to track access pattern
to an mlocked area.
>
> > + !page_rmapping(page))
>
> Not sure, does this skip SwapCache pages? Is there any point in
> calculating their idleness?
A SwapCache page may be mapped, and if it is we should not skip it. If
it is unmapped, we have nothing to do.
Regarding idleness of SwapCache pages, I think we shouldn't
differentiate them from other user pages here, because a shmem/anon page
can migrate to-and-fro the swap cache occasionally during a
memory-active workload, and we don't want to lose its idle status then.
>
> > + return;
> > +
> > + need_lock = !PageAnon(page) || PageKsm(page);
> > + if (need_lock && !trylock_page(page))
> > + return;
> > +
> > + rmap_walk(page, &rwc);
> > +
> > + if (need_lock)
> > + unlock_page(page);
> > +}
[...]
> > @@ -1754,6 +1754,11 @@ static void __split_huge_page_refcount(struct page
> > *page,
> > /* clear PageTail before overwriting first_page */
> > smp_wmb();
> >
> > + if (page_is_young(page))
> > + set_page_young(page_tail);
> > + if (page_is_idle(page))
> > + set_page_idle(page_tail);
> > +
>
> Why not in the block above?
>
> page_tail->flags |= (page->flags &
> ...
> #ifdef CONFIG_WHATEVER_IT_WAS
> 1 << PG_idle
> 1 << PG_young
> #endif
Too many ifdef's :-/ Note, the flags can be in page_ext, which mean we
would have to add something like this
#if defined(CONFIG_WHATEVER_IT_WAS) && defined(CONFIG_64BIT)
1 << PG_idle
1 << PG_young
#endif
<...>
#ifndef CONFIG_64BIT
if (page_is_young(page))
set_page_young(page_tail);
if (page_is_idle(page))
set_page_idle(page_tail);
#endif
which IMO looks less readable than what we have now.
Thanks,
Vladimir
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