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Tue, 16 Dec 2025 11:32:59 +0800 Message-ID: <1a0001cd-c38d-403b-b3ef-d19e85acd772@linux.alibaba.com> Date: Tue, 16 Dec 2025 11:32:58 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/3] arm64: mm: support batch clearing of the young flag for large folios To: Lorenzo Stoakes Cc: akpm@linux-foundation.org, david@kernel.org, catalin.marinas@arm.com, will@kernel.org, ryan.roberts@arm.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, riel@surriel.com, harry.yoo@oracle.com, jannh@google.com, willy@infradead.org, baohua@kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <5039c6a2-09b6-4c9b-accb-26583ba120db@lucifer.local> From: Baolin Wang In-Reply-To: <5039c6a2-09b6-4c9b-accb-26583ba120db@lucifer.local> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: 5bm3xk1cy9x3ot6k3gj9wrrrdbg7a9q6 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 6903C2000B X-Rspam-User: X-HE-Tag: 1765855984-726829 X-HE-Meta: U2FsdGVkX1/6P0Jv18jzEj1ZDEY5uKT9pwx/BLVc0tL9yt6tDjIg7YwbD+3OFXmc5dyF7prVHvd0IXgAdLEs6mueMIlpnfTCAXT4IK6Uvn2CsLurRFdbzf21CUHjw/CRd726NWciVPBW0tHaMP0R8/et34yipEma5b6II+plZFCPwezCHnc2x3DfFLoANPV4GItczVyi2ZiNXuZdP8ahtb44Q/SlFUZqXT+QqKYIB51jmtNooA39ZBzgBkwcdVa6zuZvO2gB0ky++Q9Pzediw1PdV80ofG4R9LaLtH+4YTP3nUy7iGd6szVaUC4TAnEs3y9sAezjNkKT26nvi7L/zjde3cNznRFsGPNVAXpqv+ylS8XUae2MA0haDyjDpxv0+75ViLEC01UoK7odKuKZDm0YiUt83XyxPx3o5YN1eNDKxgQYAAWHBKdOBo6yIUWCxe9zeJu1zFJTD2GzJBXaBhd4luv6SFGF10RRf88HO8KXtqH1477IjAoCMCapy30o1y/8EomKK+2as/JfdMYbVxcmSklfAGhQbYEDMVBkrz+1/Htuk8Qgopzrfj3Xc+P456V+VwJLj8VV1BIlBQDUwqatProZW98iZzFlE+kSxJwFrodPtDUwJ8eZgmYLWa6TXv3BYpIZihTYuGwmXFvN6PQPXMV2aV2+usnXL7dls0/zsR2+sqg54AwQ7XzxayWWE2Mjuaqqvr2MO+WUvG+qsR1FoCIM1r5uuWPq0ICEyNxPF25iMQnqSBgf/q2crvGregsxFxFLYYu5bpObW3infoacStdZJ9MJLwV9Sdheo5AVd62BhFxZipyvyF+xTSFcC/RBIvSluTFtQ59i//PxWC6epIP7j7XwvVNIvRGjwuazWTpytsaY3Y6AxQsqfGdgr5YQKSpMnPCBcbxXBMLwSdZ+QoS/Vt/kaDBmsDz1wX9MBnSCLSViSElYpctZ/vTI5jUpHKZmuNIHssRQS3q wmOdhj76 RzT4SAxpSVcey/FHtJhSRvD2nnD920h6GO9W/7Cz3+/XkmAviVOcroc2pTPGjbXA4xOewSigJZqMRjcBs5Uy2OsEcy5Re8+4SAaCzUFp30/3sRreNLcAIr8L39IR7nMQf4RoJd9xePXMYd+KJFp/tqQrClRmd0TD+TIk6GoSdkONVuyR9Dw1o8wTToeob0okLXSB7ZDKVBgZU4nVHWmAKDjXGTc7q3pz/q5//XFuPU+2wenkccdBUiUGdVcXoiDNcKAoAcUeJ4Bcx6SydPgx/w7LIuqRsGTDPBJBwa5Qn+7ZVcuw= 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 2025/12/15 19:36, Lorenzo Stoakes wrote: > On Thu, Dec 11, 2025 at 04:16:54PM +0800, Baolin Wang wrote: >> Currently, contpte_ptep_test_and_clear_young() and contpte_ptep_clear_flush_young() >> only clear the young flag and flush TLBs for PTEs within the contiguous range. >> To support batch PTE operations for other sized large folios in the following >> patches, adding a new parameter to specify the number of PTEs. >> >> While we are at it, rename the functions to maintain consistency with other >> contpte_*() functions. >> >> Signed-off-by: Baolin Wang >> --- >> arch/arm64/include/asm/pgtable.h | 12 ++++----- >> arch/arm64/mm/contpte.c | 44 ++++++++++++++++++++++---------- >> 2 files changed, 37 insertions(+), 19 deletions(-) >> >> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h >> index 0944e296dd4a..e03034683156 100644 >> --- a/arch/arm64/include/asm/pgtable.h >> +++ b/arch/arm64/include/asm/pgtable.h >> @@ -1679,10 +1679,10 @@ extern void contpte_clear_full_ptes(struct mm_struct *mm, unsigned long addr, >> extern pte_t contpte_get_and_clear_full_ptes(struct mm_struct *mm, >> unsigned long addr, pte_t *ptep, >> unsigned int nr, int full); >> -extern int contpte_ptep_test_and_clear_young(struct vm_area_struct *vma, >> - unsigned long addr, pte_t *ptep); >> -extern int contpte_ptep_clear_flush_young(struct vm_area_struct *vma, >> - unsigned long addr, pte_t *ptep); >> +extern int contpte_test_and_clear_young_ptes(struct vm_area_struct *vma, >> + unsigned long addr, pte_t *ptep, unsigned int nr); >> +extern int contpte_clear_flush_young_ptes(struct vm_area_struct *vma, >> + unsigned long addr, pte_t *ptep, unsigned int nr); > > In core mm at least, as a convention, we strip 'extern' from header declarations > as we go as they're not necessary. Sure. I can remove the 'extern'. > I wonder about this naming convention also. The contpte_xxx_() prefix > obviously implies we are operating upon PTEs in the contiguous range, now > we are doing something... different and 'nr' is a bit vague. > > Is it the nr of contiguous ranges? Well in reality it's nr_pages right? But Yes, 'nr' here means nr_pages, which follows the convention of the parameters in contpte_xxx_() functions. > now we're not saying they're necessarily contiguous in the sense of contpte... > > I wonder whether we'd be better off introducing a new function that > explicitly has 'batch' or 'batched' in the name, and have the usual > contpte_***() stuff and callers that need batching using a new underlying helper? OK. I get your point. However, this is outside the scope of my patchset. Perhaps we can clean up all the contpte_xxx_() functions if everyone agrees that this is confusing. > Obviously I defer to Ryan on all this, just my thoughts... > >> extern void contpte_wrprotect_ptes(struct mm_struct *mm, unsigned long addr, >> pte_t *ptep, unsigned int nr); >> extern int contpte_ptep_set_access_flags(struct vm_area_struct *vma, >> @@ -1854,7 +1854,7 @@ static inline int ptep_test_and_clear_young(struct vm_area_struct *vma, >> if (likely(!pte_valid_cont(orig_pte))) >> return __ptep_test_and_clear_young(vma, addr, ptep); >> >> - return contpte_ptep_test_and_clear_young(vma, addr, ptep); >> + return contpte_test_and_clear_young_ptes(vma, addr, ptep, CONT_PTES); >> } >> >> #define __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH >> @@ -1866,7 +1866,7 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma, >> if (likely(!pte_valid_cont(orig_pte))) >> return __ptep_clear_flush_young(vma, addr, ptep); >> >> - return contpte_ptep_clear_flush_young(vma, addr, ptep); >> + return contpte_clear_flush_young_ptes(vma, addr, ptep, CONT_PTES); >> } >> >> #define wrprotect_ptes wrprotect_ptes >> diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c >> index c0557945939c..19b122441be3 100644 >> --- a/arch/arm64/mm/contpte.c >> +++ b/arch/arm64/mm/contpte.c >> @@ -488,8 +488,9 @@ pte_t contpte_get_and_clear_full_ptes(struct mm_struct *mm, >> } >> EXPORT_SYMBOL_GPL(contpte_get_and_clear_full_ptes); >> >> -int contpte_ptep_test_and_clear_young(struct vm_area_struct *vma, >> - unsigned long addr, pte_t *ptep) >> +int contpte_test_and_clear_young_ptes(struct vm_area_struct *vma, >> + unsigned long addr, pte_t *ptep, >> + unsigned int nr) >> { >> /* >> * ptep_clear_flush_young() technically requires us to clear the access >> @@ -500,39 +501,56 @@ int contpte_ptep_test_and_clear_young(struct vm_area_struct *vma, >> * having to unfold. >> */ > > Hmm shouldn't you need to update this comment now 'nr' is a thing? E.g.: > > "And since we only create a contig range when the range is covered by a single > folio, we can get away with clearing young for the whole contig range here, so > we avoid having to unfold." I think the original comments are still clear: " /* * ptep_clear_flush_young() technically requires us to clear the access * flag for a _single_ pte. However, the core-mm code actually tracks * access/dirty per folio, not per page. And since we only create a * contig range when the range is covered by a single folio, we can get * away with clearing young for the whole contig range here, so we avoid * having to unfold. */ " > However now you're allowing for large folios that are not contpte? > > Overall feeling pretty iffy about implementing this this way. Please see the above comments, which explain why we should do that. >> + unsigned long start = addr; >> + unsigned long end = start + nr * PAGE_SIZE; > > So now [addr, addr + nr * PAGE_SIZE) must for sure be within a single PTE > table? Caller has made sure that (see folio_referenced_one()). >> int young = 0; >> int i; >> >> - ptep = contpte_align_down(ptep); >> - addr = ALIGN_DOWN(addr, CONT_PTE_SIZE); >> + if (pte_cont(__ptep_get(ptep + nr - 1))) >> + end = ALIGN(end, CONT_PTE_SIZE); > > OK so I guess for PTE_CONT to be set, it must be aligned to CONT_PTE_SIZE, > with other PTE entries present there not having PTE_CONT set (Ryan - do > correct me if I'm wrong!) > > I guess then no worry about running off the end of the PTE table here. > > I wonder about using pte_cont_addr_end() here, but I guess you are not > intending to limit to a range here but rather capture the entire contpte > range of the end. Right. > I don't love that now a function prefixed with contpte_... can have a > condition where part of the input range is _not_ a contpte entry, or is > specified partially... Like I said above, this is outside the scope of my patchset. If Ryan also thinks we need to do some cleanups for all the contpte_xxx() functions in the contpte.c file, we can send a follow-up patchset to rename all the contpte_xxx() functions to make it clear. >> - for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE) >> - young |= __ptep_test_and_clear_young(vma, addr, ptep); >> + if (pte_cont(__ptep_get(ptep))) { >> + start = ALIGN_DOWN(start, CONT_PTE_SIZE); >> + ptep = contpte_align_down(ptep); >> + } >> + >> + nr = (end - start) / PAGE_SIZE; > > Hm don't love this reuse of input param. OK. Will use another local variable instead. > >> + for (i = 0; i < nr; i++, ptep++, start += PAGE_SIZE) >> + young |= __ptep_test_and_clear_young(vma, start, ptep); > > Again, overall find it a bit iffy that we are essentially overloading the > code with non-contpte behaviour. Let me clarify further: this is the handling logic of the contpte_xxx() functions in the contpte.c file. For example, the function contpte_set_ptes() has a parameter 'nr', which may be greater than CONT_PTES, meaning that it can handle multiple CONT_PTES range sizes of a large folio. It might be a bit confusing, and I understand this is why you want to change the 'contpte_' prefix to the 'batch_' prefix. Of course, we can hope Ryan can provide some input on this. Thanks for reviewing.