On Thu, Jul 13, 2023 at 11:57 PM Yin, Fengwei <fengwei.yin@xxxxxxxxx> wrote:
>
>
> >> - if (pageout_anon_only_filter && !folio_test_anon(folio))
> >> + /* Do not interfere with other mappings of this folio */
> >> + if (folio_mapcount(folio) != 1)
> >> continue;
> >>
> >> - VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
> >> -
> >> - if (pte_young(ptent)) {
> >> - ptent = ptep_get_and_clear_full(mm, addr, pte,
> >> - tlb->fullmm);
> >> - ptent = pte_mkold(ptent);
> >> - set_pte_at(mm, addr, pte, ptent);
> >> - tlb_remove_tlb_entry(tlb, pte, addr);
> >> - }
> >> -
> >> - /*
> >> - * We are deactivating a folio for accelerating reclaiming.
> >> - * VM couldn't reclaim the folio unless we clear PG_young.
> >> - * As a side effect, it makes confuse idle-page tracking
> >> - * because they will miss recent referenced history.
> >> - */
> >> - folio_clear_referenced(folio);
> >> - folio_test_clear_young(folio);
> >> - if (folio_test_active(folio))
> >> - folio_set_workingset(folio);
> >> +pageout_cold_folio:
> >> if (pageout) {
> >> if (folio_isolate_lru(folio)) {
> >> if (folio_test_unevictable(folio))
> >> @@ -529,8 +542,30 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
> >> arch_leave_lazy_mmu_mode();
> >> pte_unmap_unlock(start_pte, ptl);
> >> }
> >> - if (pageout)
> >> - reclaim_pages(&folio_list);
> >> +
> >> + if (pageout) {
> >> + LIST_HEAD(reclaim_list);
> >> +
> >> + while (!list_empty(&folio_list)) {
> >> + int refs;
> >> + unsigned long flags;
> >> + struct mem_cgroup *memcg = folio_memcg(folio);
> >> +
> >> + folio = lru_to_folio(&folio_list);
> >> + list_del(&folio->lru);
> >> +
> >> + refs = folio_referenced(folio, 0, memcg, &flags);
> >> +
> >> + if ((flags & VM_LOCKED) || (refs == -1)) {
> >> + folio_putback_lru(folio);
> >> + continue;
> >> + }
> >> +
> >> + folio_test_clear_referenced(folio);
> >> + list_add(&folio->lru, &reclaim_list);
> >> + }
> >> + reclaim_pages(&reclaim_list);
> >> + }
> >
> > i overlooked the chunk above -- it's unnecessary: after we split the
> > large folio (and splice the base folios onto the same LRU list), we
> > continue at the position of the first base folio because of:
> >
> > pte--;
> > addr -= PAGE_SIZE;
> > continue;
> >
> > And then we do pte_mkold(), which takes care of the A-bit.
> This patch moves the A-bit clear out of the folio isolation loop. So
> even the folio is split and loop restarts from the first base folio,
> the A-bit is not cleared. A-bit is only cleared in reclaim loop.
>
> There is one option for A-bit clearing:
> - clear A-bit of base 4K page in isolation loop and leave large folio
> A-bit clearing to reclaim loop.
>
> This patch didn't use it because don't want to introduce A-bit clearing
> in two places. But I am open about clearing base 4K page A-bit cleared in
> isolation loop. Thanks.
Sorry but why are we trying to do multiple things in one patch that I
assumed is supposed to simply fix madvise() for large anon folios? And
none of those things seems to have a clear rationale behind it.
The only patch that makes sense at the moment (or the first patch of a
series) is what I said before:
- if (folio_mapcount(folio) != 1)
+ if (folio_estimated_sharers(folio) != 1)
And probably clarify (preferrably in the comments above) this is an
estimate because we think it's a better tradeoff if we do so (less
code/overhead from checking the mapcounts of the rest of folios within
the range).
