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a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789149166; bh=iVpZfsXMVEGiEUfVriw9pLF8pscFPyVWyCdcfJ25DGc=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=iOz351Q/hnr3UJVmku9z13YS0k8WM/um8sWugkCDEQ3q8R8SlKuwrn1Y9lnc1yzMe 4FriItsqCkS5TYFvlF64mmdFpYcVXCQjR9wpBEZe7Kf2QhLpFWQynplSJmn3agr/fx PXiAeZgHdkJ/fmy8vLoM69lSaQXBV+UnzEcxamARhjEObcJrBsx2TkXcX62YwzMjxL SwrGn7bW/qrJphLTeoAyqj9cFf6u636d3MhMHvM0MKKVPNKSGUWOgaQ5yPdx+ib9Ej b6JAzN+cbNoOlbrLwew+3sDhnK/dI5sD2FRfSKXwg93F5F4n9x3RWHQtfDdv0dmPDQ O/NBvf81QRXzw== Message-ID: Date: Fri, 11 Sep 2026 19:52:38 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 3/7] proc/task_mmu: clarify shmem mapping walk conditions in smap_gather_stats() To: Suren Baghdasaryan , "Lorenzo Stoakes (ARM)" Cc: akpm@linux-foundation.org, liam@infradead.org, vbabka@kernel.org, willy@infradead.org, jannh@google.com, paulmck@kernel.org, pfalcato@suse.de, xueyuan.chen21@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org References: <20260910234737.1340642-1-surenb@google.com> <20260910234737.1340642-4-surenb@google.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 0981580008 X-Stat-Signature: aj4djqznf9fwwmutrdf3mbanaufoqp1o X-HE-Tag: 1789149167-702960 X-HE-Meta: U2FsdGVkX1+1z30bchW7s/2Os4JwonG7AiwHcR7O5frIG1Hcjda5bVeaxKF4tnkzn0EHBy2M15/3eYLxCE7yLE38roD5gxI42Xf7WSMqxVVeY9p8TswkDIL40q7hSRjMaiWe3R4FmSN+INO7A9t3Afuk5uqVkH8SQmFIfsON7TdEEpEZluNzmm5uNuC6jUH+IHWv1bH18/Kgi9a889np708ZVAY4N9Ij/S+g9J4yUdLtpO8VFjty4d2a+cB5xGMFHVrKJAdq+8DU0mr7Qe5ZKMrQgFicIUsQCPGuYHc1v/aqPw32yFzS0kWyY5wwWcnOpl/t1PCv60RJ4Ob8AZI8l+5KvuLtzl5qfTri0R0h9KE2nuVnJ2tX33LC4QHhuhkF2MNsaHX12fBvuYzqX1KhzEHdpIfTnEFBB4eCWtoPkn+zN/ttZSup96Z5ynR/+2qz5obr1Hnb565MbxigK19em0/La8TX7PCIaZtWi5cKlddDOfJWn9mxM4BB+5XhnyRM3/CeTDhQOcgcw66rd0qp8bWp6LsRY9ti9Mu++/pJ+FZTw2/5NiUGXMd0zDG79IcDvE//wmT8LB+4XitHXVWt5YefZdduJBDU8sfM/evhxrDlx4pKvJUGx6ig1n3Z6qa0vjgFfXu60hwl6vTrdtrAHrU+AQpAfTvzIzXPg1mUfCw5mhcPKWuxXudWG4JaqkOa0nsOOIEx6AhcHt06r4tg0HmFPdW3xEnuui42sZ/U+ZKTNMR2ATOJGgzfbKvELquj/w48mhxkSbeEgP0E4VVny+MNZ2lspDWQNMeQ1IMp/oYGsaP/U/HcIfguRjUrTe8yrm8INPJGdolVsZIgu3ZYWytoC3wKS/TyuMdBraVYePy30mhhOOu/OczgXMAZagblu83TsstLkrfQ+nQzfu4CsrUEO4HjMdjCgw440xWeG02pLLRX3HzHpAqFDhbkU0sHFJk83Pk7LgIoj8M5J19 kfgzRvbS hzzCdSUlJ1FINCpFdxBTlTJV5+jJodkodx6qoYyG/+hJJ0jaek0OkKPVU8kV91N3PBh65fvX56wctVyrG2Ykjf8o+KJah7uvjcZcH+kZ+eAqzq9ezZlg/Nu/FwSWCPJ70KFwBpJBh4xPNkp2YQ8CCbkotGI4RqGikrEZKpufgdTximKaYhHQYiuOaOK8szuv58g486PdmUtxWEqBwzfE6uNs4TKc7mYaYib0NiOkMxpyafL/OvSI7sFF5jZF6AUU29x2yYv0ds4VGvyTnGafmPrCWWh0nT2uylgTbqyR/z+mNq8vYemCel78ccFAt+NXv6YycpAZB/VyJhx0UL9mCw3n6/PFggzztb6kfsJJsDCLBnH2tQxjgsyZ1uKlOCWsAZ7o7UDHl4Ziwqmxx/bqSoxObrRVAOmTsdJL8Zz7qj2CHnZ8= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/11/26 19:39, Suren Baghdasaryan wrote: > On Fri, Sep 11, 2026 at 10:10 AM Lorenzo Stoakes (ARM) wrote: >> >> On Fri, Sep 11, 2026 at 04:58:40PM +0000, Suren Baghdasaryan wrote: >>> >>> Well, the "other" Lorenzo does not agree with you and suggested this >>> approach in [1]. Specifically, see the comment: >>> ``` >>> I also don't love that 0 is taken to be 'start from vma->vm_start' and I >>> also don't love that the code in smap_gather_stats() actually special cases >>> this... >> >> I'm not sure what part of this is disagreement? >> >> It's saying passing 0 is a hack, which is one that is still in place and which >> this patch makes worse, because instead of explicitly calling out the invalid >> value, you're treating it as if it were valid. >> >>> >>> How about passing last_vma_end and making smap_gather_stats() more sane? In >>> the other invocation of smap_gather_stats() we could pass vma->vm_start >>> here. >> >> Yup, well me of 3 months ago should have suggested what I suggested re: wrapper >> (I think you cut that suggestion out of my reply). >> >>> ``` >>> >>> [1] https://lore.kernel.org/all/aifO_rCurVhFRTcl@lucifer/ >> >>> >>> >>> See [1]. This is exactly how you wrote it at the end of that reply. >> >> Assuming you passed vma->vm_start, not 0? Passing 0 makes it really strange. > > Ah! Now I see the problem you are pointing out. Ok, in v2 [2] this was > done correctly and that's the way you want it! > Okay, I agree this split was incorrect. I think I'll move is_partial > conversion completely into the next patch and this one will only > update the comment and use vma_is_cow_mapping() instead of open-coding > it. Ah, that makes sense, I missed that as I was mostly focusing on the cow stuff only. -- Cheers, David