On 7/14/2023 11:41 PM, Yu Zhao wrote:
> 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)
Definitely. As I replied to you, I will split the patch to two parts:
- just bug fixing. Include the filio_mapcount() -> folio_estimated_shares().
And using ptep_clear_flush_young_notify() to clear the young of PTEs.
- refactor for large folio.
Let me know if this is OK. Thanks.
Regards
Yin, Fengwei
>
> 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).
