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b=lJimFy3X/ep7ZSi2QaKlVNTJ6kglkHTPykSY513m05guI88+vbz/L+C0vQE4INe07 c7OTNGE6TYmqojp2BlFWhUDgJCkJ6wNMWbZbjxlqrTg2TTAiRgUhC1LAnYdkNqQ+SS PDtVehOv3x6iIYOC21dFd7JdD49RJwdTADiX+hRvb+v53oAbuIVLcPq0t4sK82qHhE Hb90laTMWpqdc9N5fTChYDsqoa6zBGv7SZR2WdNDbgEErSlLziEe9Bc6cSlcb/9gqP NdjFZ/W81ptX2HYNznqUonr6EMdyOE8K6QQKHrlgxUdSO2PpymJnIa/Z6JlrfG26F4 vlqfAlOGwLQTg== Message-ID: Date: Mon, 11 May 2026 10:59:35 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/9] mm/rmap: refactor hugetlb pte clearing in try_to_unmap_one To: Dev Jain , akpm@linux-foundation.org, ljs@kernel.org, hughd@google.com, chrisl@kernel.org, kasong@tencent.com Cc: riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, qi.zheng@linux.dev, shakeel.butt@linux.dev, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, rppt@kernel.org, surenb@google.com, mhocko@suse.com, baolin.wang@linux.alibaba.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, youngjun.park@lge.com, pfalcato@suse.de, ryan.roberts@arm.com, anshuman.khandual@arm.com References: <20260506094504.2588857-1-dev.jain@arm.com> <20260506094504.2588857-3-dev.jain@arm.com> <5a4c3c3d-66c8-4ef6-bb6a-2ec0e32694a1@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: na8zi8scin1txm78g48bb6txnezhoxuh X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: AD12B40006 X-Rspam-User: X-HE-Tag: 1778489983-658724 X-HE-Meta: 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 Cl5FODFv 0Vz7CR2YvyWbVOLeC+CZb3qc2rg5avpLrTRvNbzg3MGL4P9BBTjbA3gon4lNnZd9deV7nfDhAnw0lTQq54185MMi1w+6QmLxKixtIRQdtXvRFExabK9kd/KsM2cHE/bNNmeMFsaa0ymq7NjtV+DGMT2tjKYzdQgGVTtJHN7S1NgvXl6JlRuLSZmozmBI56M0aXEbSVwE0qeLOo0QUdmG4+xOzm2QbbholhX+LBggQhuaLIhIV9Q/wA+SsPReor9gg6GngLsUWjZG+UKXNdHE0JUhFwUlgPMeh8Ibi5QnfvrL5lUlQzHlJ3kXzHguHdazMglbja2nT1b8WOIRf4yFgxEBZH0Mb6B565WW3CDTrsgoI/eBGjj73x6NXmpJl3/+v8PCoPvaGFRERM5I= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/11/26 10:53, Dev Jain wrote: > > > On 11/05/26 12:40 pm, David Hildenbrand (Arm) wrote: >> On 5/6/26 11:44, Dev Jain wrote: >>> Simplify the code by refactoring the folio_test_hugetlb() branch into >>> a new function. >>> >>> While at it, convert BUG helpers to WARN helpers. >>> >>> Signed-off-by: Dev Jain >>> --- >>> mm/rmap.c | 117 ++++++++++++++++++++++++++++++++---------------------- >>> 1 file changed, 69 insertions(+), 48 deletions(-) >>> >>> diff --git a/mm/rmap.c b/mm/rmap.c >>> index a5f067a09de0f..a98acdea0530a 100644 >>> --- a/mm/rmap.c >>> +++ b/mm/rmap.c >>> @@ -1978,6 +1978,68 @@ static inline unsigned int folio_unmap_pte_batch(struct folio *folio, >>> FPB_RESPECT_WRITE | FPB_RESPECT_SOFT_DIRTY); >>> } >>> >>> +/* Returns false if unmap needs to be aborted */ >>> +static inline bool unmap_hugetlb_folio(struct vm_area_struct *vma, >> >> I'm wondering whether we should make it clearer that this belongs to the >> try_to_unmap family by calling it >> >> ttu_hugetlb_folio > > Yes I had suggested a ttu_ prefix somewhere else in the first version, > Lorenzo didn't like it (or probably he didn't like that specific use > of ttu): > > https://lore.kernel.org/all/a8b06f36-98e1-435c-881f-67242bc4304a@lucifer.local/ > > Don't know about a better name other than "commit_ttu_lazyfree_folio" in > that case, but for the hugetlb case, I like ttu_hugetlb_folio. Yes, in particular, once we just process the whole hugetlb oddity in there. I don't really care about the exact name as long as it's clear that this is not something fairly generic. [...] >> >> >>> + /* >>> + * huge_pmd_unshare may unmap an entire PMD page. >>> + * There is no way of knowing exactly which PMDs may >>> + * be cached for this mm, so we must flush them all. >>> + * start/end were already adjusted above to cover this >>> + * range. >>> + */ >>> + flush_cache_range(vma, range->start, range->end); >>> + >>> + /* >>> + * To call huge_pmd_unshare, i_mmap_rwsem must be >>> + * held in write mode. Caller needs to explicitly >>> + * do this outside rmap routines. >>> + * >>> + * We also must hold hugetlb vma_lock in write mode. >>> + * Lock order dictates acquiring vma_lock BEFORE >>> + * i_mmap_rwsem. We can only try lock here and fail >>> + * if unsuccessful. >>> + */ >>> + if (!folio_test_anon(folio)) { >>> + struct mmu_gather tlb; >>> + >>> + VM_WARN_ON(!(flags & TTU_RMAP_LOCKED)); >>> + if (!hugetlb_vma_trylock_write(vma)) { >>> + *exit_walk = true; >>> + return false; >>> + } >>> + >>> + tlb_gather_mmu_vma(&tlb, vma); >>> + if (huge_pmd_unshare(&tlb, vma, pvmw->address, pvmw->pte)) { >>> + hugetlb_vma_unlock_write(vma); >>> + huge_pmd_unshare_flush(&tlb, vma); >>> + tlb_finish_mmu(&tlb); >>> + /* >>> + * The PMD table was unmapped, >>> + * consequently unmapping the folio. >>> + */ >>> + *exit_walk = true; >>> + return true; >>> + } >>> + hugetlb_vma_unlock_write(vma); >>> + tlb_finish_mmu(&tlb); >>> + } >>> + *pteval = huge_ptep_clear_flush(vma, pvmw->address, pvmw->pte); >>> + if (pte_dirty(*pteval)) >>> + folio_mark_dirty(folio); >>> + >>> + *exit_walk = false; >>> + return true; >> >> >> Can we instead introduce some enum that tells the caller how to proceed? >> >> I assume we have >> >> (a) Abort walk (ret = false + page_vma_mapped_walk_done()) >> >> (b) Walk done (ret = true + page_vma_mapped_walk_done()) >> >> (c) Continue walk (call page_vma_mapped_walk()) >> >> enum ttu_walk_result { >> TTU_WALK_CONTINUE, >> TTU_WALK_ABORT, >> TTU_WALK_DONE >> } > > I had replied to such a suggestion here: > > https://lore.kernel.org/all/caa7c455-7472-48eb-a5dc-145e587d67ba@arm.com/ > > Probably we don't have any other solution : ) That looks like the right way to. The boolean return is just nasty. >>> - */ >>> - goto walk_done; >>> - } >>> - hugetlb_vma_unlock_write(vma); >>> - tlb_finish_mmu(&tlb); >>> + ret = unmap_hugetlb_folio(vma, folio, &pvmw, subpage, >>> + flags, &pteval, &range, >>> + &exit_walk); >>> + if (exit_walk) { >>> + page_vma_mapped_walk_done(&pvmw); >>> + break; >> >> In the old walk_abort case you wouldn't set ret = false? > > ret will be set appropriately in unmap_hugetlb_folio. Ah, right. Confusing ;) >> >> When returning the enum you could simply do something like >> >> switch (ret) { >> case TTU_WALK_ABORT: >> goto walk_abort; >> case TTU_WALK_DONE: >> goto walk_done; >> default: >> break; >> } >> >> >> While I like this patch, can we please just move all the hugetlb shite into this >> helper function? >> >> Essentially, get rid of hugetlb special casing in the remainder of the function. >> >> That also makes the function name clearer (right now it's only doing a part of >> hugetlb folio unmapping). > > Okay I can try that. That would mean splitting the pvmw walk for hugetlb and > non-hugetlb, but I suspect it would be very less code duplication. Right, and it would also be clearer that hugetlb really only is called for hwpoison handling. -- Cheers, David