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Scan all pages in a to-be-split folio to >>>> determine which after-split folios need the flag. >>>> >>>> An alternatives is to change PG_has_hwpoisoned to PG_maybe_hwpoisone= d to >>>> avoid the scan and set it on all after-split folios, but resulting f= alse >>>> positive has undesirable negative impact. To remove false positive, = caller >>>> of folio_test_has_hwpoisoned() and folio_contain_hwpoisoned_page() n= eeds to >>>> do the scan. That might be causing a hassle for current and future c= allers >>>> and more costly than doing the scan in the split code. More details = are >>>> discussed in [1]. >>>> >>>> It is OK that current implementation does not do this, because memor= y >>>> failure code always tries to split to order-0 folios and if a folio = cannot >>>> be split to order-0, memory failure code either gives warnings or th= e split >>>> is not performed. >>>> >>> >>> We're losing PG_has_hwpoisoned for large folios, so likely this shoul= d be >>> a stable fix for splitting anything to an order > 0 ? >> >> I was the borderline on this, because: >> >> 1. before the hotfix, which prevents silently bumping target split ord= er, >> memory failure would give a warning when a folio is split to >0 or= der >> folios. The warning is masking this issue. >> 2. after the hotfix, folios with PG_has_hwpoisoned will not be split >> to >0 order folios since memory failure always wants to split a fo= lio >> to order 0 and a folio containing LBS folios will not be split, th= us >> without losing PG_has_hwpoisoned. >> > > I was rather wondering about something like > > a) memory failure wants to split to some order (order-0?) but fails the= split (e.g., raised reference). hwpoison is set. > > b) Later, something else (truncation?) wants to split to order > 0 and = loses the hwpoison bit. > > Would that be possible? Yeah, that is possible after commit 7460b470a131 ("mm/truncate: use folio= _split() in truncate operation") when truncation splits a folio to >0 order folios= =2E > >> >> I will add >> Fixes: c010d47f107f ("mm: thp: split huge page to any lower order page= s") >> and cc stable in the next version. > > That would be better I think. But then you have to pull this patch out = as well from this series, gah :) Yep, let me tell this horrible story in the cover letter. -- Best Regards, Yan, Zi