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From: Lance Yang In-Reply-To: <8FF0358E-1ECE-42DA-AE4B-8D5A578450EC@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Stat-Signature: xy3tmw4im7hi3us7b98pn4aqmsb3d4b4 X-Rspamd-Queue-Id: D22BF100006 X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1759632285-208573 X-HE-Meta: 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 6Tsh0CII R4NjCKsvBwz6GckdMEFMCdTgMOrSzIy2TP3nJAhfWwYzqmfNjDeuV9FUJk+iCYHxSpu+Ue8agal5PYs3sE3DtnXdm/zdQ2VV5DAMLPWw/4qkRplsTUK9660QNzBtA8FBdcbf3hJLyD0m8yAXP0z7l1PXhvu/qbRAkg4WUff8PocdW2/SqN84FgEj2OdDxvMFYUfn6bRXpPO+eKrXN99a32flF23Z9ZO+lQ+PU5fOVSoMjDb7s5r0zRqpuvKKdQW/OlRcl22OBtSMpOOi1ZdqhhS5UORIgp7dYIOv/oifGL1hlnumeOXCH6qB3Cw== 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 2025/10/5 10:38, Zi Yan wrote: > On 4 Oct 2025, at 22:35, Lance Yang wrote: > >> On 2025/10/4 21:11, Dev Jain wrote: >>> >>> On 04/10/25 3:12 pm, Wei Yang wrote: >>>> On Fri, Oct 03, 2025 at 10:35:12PM +0530, Dev Jain wrote: >>>>> On 02/10/25 1:02 pm, Lance Yang wrote: >>>>>> From: Lance Yang >>>>>> >>>>>> As David suggested, the PTE scanning logic in hpage_collapse_scan_pmd() >>>>>> and __collapse_huge_page_isolate() was almost duplicated. >>>>>> >>>>>> This patch cleans things up by moving all the common PTE checking logic >>>>>> into a new shared helper, thp_collapse_check_pte(). >>>>>> >>>>>> Suggested-by: David Hildenbrand >>>>>> Signed-off-by: Lance Yang >>>>>> --- >>>>> In hpage_collapse_scan_pmd(), we enter with mmap lock held, so for >>>> This is true for the first loop, but we will unlock/lock mmap and revalidate >>>> vma before isolation. >>>> >>>>> an anonymous vma, is it even possible to hit if (! folio_test_anon(folio))? >>>>> In which case we can replace this with VM_BUG_ON_FOLIO and abstract away >>>>> till the folio_maybe_mapped_shared() block? >>>> But it looks still valid, since hugepage_vma_revalidate() will check the vma >>>> is still anonymous vma after grab the mmap lock again. >>>> >>>> My concern is would VM_BUG_ON_FOLIO() be too heavy? How about warn on and >>>> return? >>> >>> Frankly I do not have much opinion on the BUG_ON/WARN_ON debate since I haven't >>> properly understood that, but this BUG_ON is under CONFIG_DEBUG_VM anways. But >> >> Yeah, VM_BUG_ON_FOLIO() is under CONFIG_DEBUG_VM, so it won't affect >> production kernels. > > Many distros enable it by default. For mm, we are moving away from > using BUG_ON or VM_BUG_ON. No need to crash the system if it is possible > to handle it gracefully. Ah, good to know that, thanks! > >> >>> if you want to change this to WARN then you can do it at both places. >> >> It should flag such an impossible condition there during development. >> So, I'd prefer to stick with VM_BUG_ON_FOLIO(). >> >> @Wei please let me know if you feel strongly otherwise :) > > > -- > Best Regards, > Yan, Zi