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 q24lFFdv ym5aXK0Q5jHk9Z2XRyH/omCBca3tppdwJrqOQ1HEAUX0zjCVib25ensPjdfe0Tgpe4kPcDpgjQzTDyEqXsXap/C9JpF/fmoQsTHrDTB0C0iJsWXlYOnoIESpAzgpjXuy+GXRZNO9dZFTTvQcQ2YqD5v2/+GY6EFNawxvT/x+gMSK2tSRcmvODbs0AXXbK9nR/NfD5MawvibGaLuIOuJiiY74Ypk2KTHp4ShpqOyigeGj16AFCpYomIfIVYDuuCTnkMaOMuwyZzw26p0nYsboKpD+lPMfjjbuKtQvE+Fak+pEoE3PVUFB1RfAMTyD5/1z4pn0M7B66MlVRF6Y40RAapBBYqA/w1O+CXbAV6IxoBq9lNHaSsFexZWoNsj/ySom7LrrbNUFPDwkK9u2imCdjAeoXHB4zDMdIRu7iVzF7LR9S9GQ1KIG27N/0vw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 27 Aug 2026, at 11:23, David Hildenbrand (Arm) wrote: > On 8/26/26 18:20, Kiryl Shutsemau wrote: >> From: "Kiryl Shutsemau (Meta)" >> >> deferred_split_isolate() probes each queued folio with folio_try_get()= =2E >> folio_try_get() failure is treated as a lost race with folio_put(): cl= ear >> PG_partially_mapped, correct MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, take >> the folio off the queue. >> >> The folio_put() race is the most common case for !folio_try_get(), but= >> it is not the only option. Another scenario is folio_ref_freeze(). >> >> A zero refcount in such cases does not mean the folio is going away. = It >> means "don't touch me" and current deferred_split_isolate() doesn't >> respect it. It can lead to unqueueing folios from the deferred list fo= r >> no reason: > > Yes. > >> >> CPU 0 CPU 1 >> --------------------------- ------------------------------ >> freeze a mapped folio deferred_split_scan() >> folio_ref_freeze() folio_try_get() fails >> folio_clear_partially_mapped() >> NR_ANON_PARTIALLY_MAPPED-- >> folio off the queue >> give up, put it back >> folio_ref_unfreeze() >> >> The folio is still partially mapped, but it is no longer a split candi= date. >> Nothing queues it again until part of it is unmapped once more. >> >> Skip the folio instead: whoever freezes the folio, owns it and owner i= s >> responsible for its fate. It also covers the folio_put() case: >> __folio_put() unqueues the folio via folio_unqueue_deferred_split(). >> >> Reported-by: Lance Yang >> Link: https://lore.kernel.org/all/20260824131224.73344-1-lance.yang@li= nux.dev/ > > Fixes? > >> Assisted-by: Claude-Code:claude-opus-5 >> Signed-off-by: Kiryl Shutsemau (Meta) >> --- >> mm/huge_memory.c | 19 ++++--------------- >> 1 file changed, 4 insertions(+), 15 deletions(-) >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index ced400f72d43..6281ed993243 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -4590,22 +4590,11 @@ static enum lru_status deferred_split_isolate(= struct list_head *item, >> struct folio *folio =3D container_of(item, struct folio, _deferred_l= ist); >> struct list_head *freeable =3D cb_arg; >> >> - if (folio_try_get(folio)) { >> - list_lru_isolate_move(lru, item, freeable); >> - return LRU_REMOVED; >> - } >> + /* Lost race to folio_put() or the folio is under folio_ref_freeze()= */ >> + if (!folio_try_get(folio)) >> + return LRU_SKIP; >> >> - /* >> - * We lost race with folio_put(). Read folio state before the >> - * isolate: folio_unqueue_deferred_split() checks list_empty() >> - * locklessly, so once removed the folio can be freed any time. >> - */ >> - if (folio_test_partially_mapped(folio)) { >> - folio_clear_partially_mapped(folio); >> - mod_mthp_stat(folio_order(folio), >> - MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1); >> - } >> - list_lru_isolate(lru, item); >> + list_lru_isolate_move(lru, item, freeable); >> return LRU_REMOVED; >> } >> > > Who will clean up the stats that we used to clean up? That should be me= ntioned > in the commit log, otherwise it looks like some piece of the puzzle is = missing. It is kinda implied in the last paragraph in the commit log (copied below= ), but I agree that stating it explicitly is better. |> Skip the folio instead: whoever freezes the folio, owns it and owner i= s |> responsible for its fate. It also covers the folio_put() case: |> __folio_put() unqueues the folio via folio_unqueue_deferred_split(). Best Regards, Yan, Zi