From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1986C3BE16F for ; Mon, 11 May 2026 08:59:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778489983; cv=none; b=sYa5PB+kLSJjzbP1veUU7NMulj3QeP8uniBR9oO2IoLk5+b7XGRz8qJXaeN4EIvlTBl3ZHRx6YUoaTLaWB7IjPiaNxoPVBTd8D25aXKX+/U0vfm4vCsBJ/Z1UWMls6BVcbAjzQeVh90YvwAJG2bFIo4pHrvhj9vr+3r7l/TbrII= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778489983; c=relaxed/simple; bh=4GymnGq3ZLjKJIR22N12zMnTywRK44ioF56s34ZZC5E=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=rkGkfI4zpbNV1QkyGRLtERJfggZ3mIxf+X+4L68And0aXLKxEsKr79O7+f1HDwO/ZWuWvKkrfQiRmZa0nYugItvVVAj9v+eSRyQzbn2asSmS8wkX18dZGzt+a7iV1YkHqNdOuSrPD4iwVR9QsXxD2OHu8ppCJQQPrJ9R9oxmArU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=lJimFy3X; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="lJimFy3X" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 50192C2BCC9; Mon, 11 May 2026 08:59:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778489982; bh=4GymnGq3ZLjKJIR22N12zMnTywRK44ioF56s34ZZC5E=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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