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 B4E663B0AE5 for ; Mon, 11 May 2026 08:16:54 +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=1778487414; cv=none; b=sD5avulP+Nt7zOJa49hw5MVCqNXMriuthr1agX2utLb+Af++5A9WWdz9JaZRnqbNmYxlc/a8x7xfbdAZTCYPzMrloGPNt/AIedHNqevOxMJWmjM/rsN1lBRkp+z5YcEe8QC/Iksi/B7jPjf6p3ceLUu7j5VUw7O899KDsEAF0k4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778487414; c=relaxed/simple; bh=SxUqt7uD6fVUEKRkwZWsVK4iqdIk9wMXj1vmjYOzTzo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=iN/G7iG301m8gcSjhK2AaPmKQskDwECse/04lJuhGSRrGchI5tcprvjtEJPldub4Vg5hoThELi9lzlOrd/8LUsmYLkjIL6YENsPxqGoGXaa6k1DhuJI8Gi/7MvoeFXzhZskPzsGpqOb/b8EzQlPrJBGASFvTwCtHBDRKmJGOy08= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=AWKQsPTO; 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="AWKQsPTO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D822EC2BCB0; Mon, 11 May 2026 08:16:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778487414; bh=SxUqt7uD6fVUEKRkwZWsVK4iqdIk9wMXj1vmjYOzTzo=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=AWKQsPTOihmweFbrBtoncGSoxFz5BuWlzbjR45E5E0xALIuZ5h616sSVfgxni+dIj AvEGM4+HqWHVaHnLpB19BWuQEnHbPS6GB/w7/n/Rbb9/64axEZogoT2ncT5ne9/he5 InzFQd/qI+H8KvHs4nvWjYcBqLqPHmmBCjxog5h5e46mi2oCogFKZAv4lw6gironIN +rv81VuSIzd8PE0BLdDTvWORMPPvFsNmtgYl0Jn324hgSBUHQVJVcyco7rvgwCRTtm v+bCOKoGrd2VrarlVB3IBs6Lwrii+S3RVHFtHNO1JtVOzeOhF3971EkuG9etvL909V N7ndQGvfEfPWQ== Message-ID: Date: Mon, 11 May 2026 10:16:47 +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 9/9] mm/rmap: enable batch unmapping of anonymous folios 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> <20260506094504.2588857-10-dev.jain@arm.com> 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 5/6/26 11:45, Dev Jain wrote: > Enable batch clearing of ptes, and batch swap setting of ptes for anon > folio unmapping. > > Processing all ptes of a large folio in one go helps us batch across > atomics (add_mm_counter etc), barriers (in the function > __folio_try_share_anon_rmap), repeated calls to page_vma_mapped_walk(), > to name a few. In general, batching helps us to execute similar code > together, making the execution of the program more memory and > CPU friendly. > > On arm64-contpte, batching also helps us avoid redundant ptep_get() calls > and TLB flushes while breaking the contpte mapping. > > The handling of anon-exclusivity is very similar to commit cac1db8c3aad > ("mm: optimize mprotect() by PTE batching"). Since folio_unmap_pte_batch() > won't look at the bits of the underlying page, we need to process > sub-batches of ptes pointing to pages which are same w.r.t exclusivity, > and batch set only those ptes to swap ptes in one go. Hence export > page_anon_exclusive_sub_batch() to internal.h and reuse it. > > arch_unmap_one() is only defined for sparc64; I am not comfortable > regarding the nuances between retrieving the pfn from pte_pfn() or from > (paddr = pte_val(oldpte) & _PAGE_PADDR_4V). > > (And, pte_next_pfn() can't even be called from arch_unmap_one() because > that file does not include pgtable.h) So just disable the > "sparc64-anon-swapbacked" case for now. > > We need to take care of rmap accounting (folio_remove_rmap_ptes) and > reference accounting (folio_put_refs) when anon folio unmap succeeds. > In case we partially batch the large folio and fail, we need to correctly > do the accounting for pages which were successfully unmapped. So, put > this accounting code in __unmap_anon_folio() itself, instead of doing > some horrible goto jumping at the callsite of unmap_anon_folio(). > > Add a comment at relevant places to say that we are on a device-exclusive > entry and not a present entry. > > If the batch length is less than the number of pages in the folio, then > we must skip over this batch. > > The page_vma_mapped_walk API ensures this - check_pte() will return true > only if any of [pvmw->pfn, pvmw->pfn + nr_pages) is mapped by the pte. > There is no pfn underlying a swap pte, so check_pte returns false and we > keep skipping until we hit a present pte, which is where we want to start > unmapping from next. > This patch is doing too much. Please separate the cleanups (e.g., moving stuff into helpers -- that likely should have a ttu_ prefix) from the real deal. -- Cheers, David