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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , "Matthew Wilcox (Oracle)" , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Pankaj Raghav Subject: Re: [PATCH v2 1/3] mm/huge_memory: do not change split_huge_page*() target order silently. 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 16 Oct 2025, at 3:31, Wei Yang wrote: > On Wed, Oct 15, 2025 at 11:34:50PM -0400, Zi Yan wrote: >> Page cache folios from a file system that support large block size (LB= S) >> can have minimal folio order greater than 0, thus a high order folio m= ight >> not be able to be split down to order-0. Commit e220917fa507 ("mm: spl= it a >> folio in minimum folio order chunks") bumps the target order of >> split_huge_page*() to the minimum allowed order when splitting a LBS f= olio. >> This causes confusion for some split_huge_page*() callers like memory >> failure handling code, since they expect after-split folios all have >> order-0 when split succeeds but in really get min_order_for_split() or= der >> folios. >> >> Fix it by failing a split if the folio cannot be split to the target o= rder. >> Rename try_folio_split() to try_folio_split_to_order() to reflect the = added >> new_order parameter. Remove its unused list parameter. >> >> Fixes: e220917fa507 ("mm: split a folio in minimum folio order chunks"= ) >> [The test poisons LBS folios, which cannot be split to order-0 folios,= and >> also tries to poison all memory. The non split LBS folios take more me= mory >> than the test anticipated, leading to OOM. The patch fixed the kernel >> warning and the test needs some change to avoid OOM.] >> Reported-by: syzbot+e6367ea2fdab6ed46056@syzkaller.appspotmail.com >> Closes: https://lore.kernel.org/all/68d2c943.a70a0220.1b52b.02b3.GAE@g= oogle.com/ >> Signed-off-by: Zi Yan >> Reviewed-by: Luis Chamberlain >> Reviewed-by: Pankaj Raghav > > Do we want to cc stable? This only triggers a warning, so I am inclined not to. But some config decides to crash on kernel warnings. If anyone thinks it is worth ccing stable, please let me know. > >> --- >> include/linux/huge_mm.h | 55 +++++++++++++++++------------------------= >> mm/huge_memory.c | 9 +------ >> mm/truncate.c | 6 +++-- >> 3 files changed, 28 insertions(+), 42 deletions(-) >> >> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h >> index c4a811958cda..3d9587f40c0b 100644 >> --- a/include/linux/huge_mm.h >> +++ b/include/linux/huge_mm.h >> @@ -383,45 +383,30 @@ static inline int split_huge_page_to_list_to_ord= er(struct page *page, struct lis >> } >> >> /* >> - * try_folio_split - try to split a @folio at @page using non uniform= split. >> + * try_folio_split_to_order - try to split a @folio at @page to @new_= order using >> + * non uniform split. >> * @folio: folio to be split >> - * @page: split to order-0 at the given page >> - * @list: store the after-split folios >> + * @page: split to @order at the given page > > split to @new_order? Will fix it. > >> + * @new_order: the target split order >> * >> - * Try to split a @folio at @page using non uniform split to order-0,= if >> - * non uniform split is not supported, fall back to uniform split. >> + * Try to split a @folio at @page using non uniform split to @new_ord= er, if >> + * non uniform split is not supported, fall back to uniform split. Af= ter-split >> + * folios are put back to LRU list. Use min_order_for_split() to get = the lower >> + * bound of @new_order. > > We removed min_order_for_split() here right? We removed it from the code, but caller should use min_order_for_split() to get the lower bound of new_order if they do not want to split to fail unexpectedly. Thank you for the review. > >> * >> * Return: 0: split is successful, otherwise split failed. >> */ >> -static inline int try_folio_split(struct folio *folio, struct page *p= age, >> - struct list_head *list) >> +static inline int try_folio_split_to_order(struct folio *folio, >> + struct page *page, unsigned int new_order) >> { >> - int ret =3D min_order_for_split(folio); >> - >> - if (ret < 0) >> - return ret; >> - >> - if (!non_uniform_split_supported(folio, 0, false)) >> - return split_huge_page_to_list_to_order(&folio->page, list, >> - ret); >> - return folio_split(folio, ret, page, list); >> + if (!non_uniform_split_supported(folio, new_order, /* warns=3D */ fa= lse)) >> + return split_huge_page_to_list_to_order(&folio->page, NULL, >> + new_order); >> + return folio_split(folio, new_order, page, NULL); >> } > > -- = > Wei Yang > Help you, Help me -- Best Regards, Yan, Zi