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[2003:cb:c705:3b00:64b8:6719:5794:bf13]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-438dcc2e384sm29647105e9.19.2025.01.29.08.44.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 29 Jan 2025 08:44:30 -0800 (PST) Message-ID: <2d0eeca2-7875-415b-b20f-cebebce70f50@redhat.com> Date: Wed, 29 Jan 2025 17:44:28 +0100 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] damon: add feature to monitor only writes To: SeongJae Park , Pedro Demarchi Gomes Cc: damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20250129055237.38547-1-sj@kernel.org> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <20250129055237.38547-1-sj@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 29.01.25 06:52, SeongJae Park wrote: > + linux-mm@ and David > > Hi Pedro, > > On Wed, 29 Jan 2025 01:40:41 -0300 Pedro Demarchi Gomes wrote: > >> Add damon operation DAMON_OPS_VADDR_WRITES to monitor only writes. > > Thank you for this patch! I think this is a successor of the patch[1] that you > posted before. Thank you very much for continuing this work. > > Nonetheless, could you please add more description about this patch including > changes you made from the previous version? I'm especially curious if the > concern[2] that David raised to the previous version is solved. The CoW concern is resolved upstream now. You can convert pte_write(pte) -> !ptw_write(pte) without risking weird interactions with DMA etc. > Motivation of > this patch including expected usage (I remeber that you mentioned using this > feature to find KSM-candidate memory regions, but I'm curious if you found more > potential usages) and test/evaluation results if available. > > Adding comments below to things that stand out to my eyes on a glance. > > [1] https://lore.kernel.org/lkml/20220203131237.298090-1-pedrodemargomes@gmail.com/ > [2] https://lore.kernel.org/dcb5d9c7-ae5c-e0c5-adee-37f5b92281e0@redhat.com > >> >> Signed-off-by: Pedro Demarchi Gomes >> --- >> include/linux/damon.h | 5 +- >> mm/damon/Makefile | 2 +- >> mm/damon/ops-common.c | 80 +++++ >> mm/damon/ops-common.h | 3 + >> mm/damon/sysfs.c | 1 + >> mm/damon/vaddr-writes.c | 735 ++++++++++++++++++++++++++++++++++++++++ >> 6 files changed, 824 insertions(+), 2 deletions(-) >> create mode 100644 mm/damon/vaddr-writes.c >> >> diff --git a/include/linux/damon.h b/include/linux/damon.h >> index af525252b853..9a6027faa7a6 100644 >> --- a/include/linux/damon.h >> +++ b/include/linux/damon.h >> @@ -485,6 +485,7 @@ struct damos { >> * enum damon_ops_id - Identifier for each monitoring operations implementation >> * >> * @DAMON_OPS_VADDR: Monitoring operations for virtual address spaces >> + * @DAMON_OPS_VADDR_WRITES: Monitoring only write operations for virtual address spaces >> * @DAMON_OPS_FVADDR: Monitoring operations for only fixed ranges of virtual >> * address spaces >> * @DAMON_OPS_PADDR: Monitoring operations for the physical address space >> @@ -492,6 +493,7 @@ struct damos { >> */ >> enum damon_ops_id { >> DAMON_OPS_VADDR, >> + DAMON_OPS_VADDR_WRITES, >> DAMON_OPS_FVADDR, >> DAMON_OPS_PADDR, >> NR_DAMON_OPS, >> @@ -846,7 +848,8 @@ int damon_select_ops(struct damon_ctx *ctx, enum damon_ops_id id); >> >> static inline bool damon_target_has_pid(const struct damon_ctx *ctx) >> { >> - return ctx->ops.id == DAMON_OPS_VADDR || ctx->ops.id == DAMON_OPS_FVADDR; >> + return ctx->ops.id == DAMON_OPS_VADDR || ctx->ops.id == DAMON_OPS_VADDR_WRITES >> + || ctx->ops.id == DAMON_OPS_FVADDR; >> } >> >> static inline unsigned int damon_max_nr_accesses(const struct damon_attrs *attrs) >> diff --git a/mm/damon/Makefile b/mm/damon/Makefile >> index 8b49012ba8c3..c3c8dce0b34a 100644 >> --- a/mm/damon/Makefile >> +++ b/mm/damon/Makefile >> @@ -1,7 +1,7 @@ >> # SPDX-License-Identifier: GPL-2.0 >> >> obj-y := core.o >> -obj-$(CONFIG_DAMON_VADDR) += ops-common.o vaddr.o >> +obj-$(CONFIG_DAMON_VADDR) += ops-common.o vaddr.o vaddr-writes.o >> obj-$(CONFIG_DAMON_PADDR) += ops-common.o paddr.o >> obj-$(CONFIG_DAMON_SYSFS) += sysfs-common.o sysfs-schemes.o sysfs.o >> obj-$(CONFIG_DAMON_RECLAIM) += modules-common.o reclaim.o >> diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c >> index d25d99cb5f2b..4a3cad303a60 100644 >> --- a/mm/damon/ops-common.c >> +++ b/mm/damon/ops-common.c >> @@ -9,6 +9,8 @@ >> #include >> #include >> #include >> +#include >> +#include >> >> #include "ops-common.h" >> >> @@ -67,6 +69,84 @@ void damon_pmdp_mkold(pmd_t *pmd, struct vm_area_struct *vma, unsigned long addr >> #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ >> } >> >> +static inline bool pte_is_pinned(struct vm_area_struct *vma, unsigned long addr, pte_t pte) >> +{ >> + struct folio *folio; >> + >> + if (!pte_write(pte)) >> + return false; >> + if (!is_cow_mapping(vma->vm_flags)) >> + return false; >> + if (likely(!test_bit(MMF_HAS_PINNED, &vma->vm_mm->flags))) >> + return false; >> + folio = vm_normal_folio(vma, addr, pte); >> + if (!folio) >> + return false; >> + return folio_maybe_dma_pinned(folio); >> +} >> + >> +static inline void clear_soft_dirty_pmd(struct vm_area_struct *vma, >> + unsigned long addr, pmd_t *pmdp) >> +{ >> + pmd_t old, pmd = *pmdp; >> + >> + if (pmd_present(pmd)) { >> + /* See comment in change_huge_pmd() */ >> + old = pmdp_invalidate(vma, addr, pmdp); >> + if (pmd_dirty(old)) >> + pmd = pmd_mkdirty(pmd); >> + if (pmd_young(old)) >> + pmd = pmd_mkyoung(pmd); >> + >> + pmd = pmd_wrprotect(pmd); >> + pmd = pmd_clear_soft_dirty(pmd); >> + >> + set_pmd_at(vma->vm_mm, addr, pmdp, pmd); >> + } else if (is_migration_entry(pmd_to_swp_entry(pmd))) { >> + pmd = pmd_swp_clear_soft_dirty(pmd); >> + set_pmd_at(vma->vm_mm, addr, pmdp, pmd); >> + } >> +} >> + >> +static inline void clear_soft_dirty(struct vm_area_struct *vma, >> + unsigned long addr, pte_t *pte) >> +{ >> + /* >> + * The soft-dirty tracker uses #PF-s to catch writes >> + * to pages, so write-protect the pte as well. See the >> + * Documentation/admin-guide/mm/soft-dirty.rst for full description >> + * of how soft-dirty works. >> + */ >> + pte_t ptent = *pte; >> + >> + if (pte_present(ptent)) { >> + pte_t old_pte; >> + >> + if (pte_is_pinned(vma, addr, ptent)) >> + return; >> + old_pte = ptep_modify_prot_start(vma, addr, pte); >> + ptent = pte_wrprotect(old_pte); >> + ptent = pte_clear_soft_dirty(ptent); >> + ptep_modify_prot_commit(vma, addr, pte, old_pte, ptent); >> + } else if (is_swap_pte(ptent)) { >> + ptent = pte_swp_clear_soft_dirty(ptent); >> + set_pte_at(vma->vm_mm, addr, pte, ptent); >> + } >> +} > > Seems you're copying code from task_mmu.c to here. Can you explain why you do > so instead of making those be able to use from other files and reuse? +1 This code should not be copied in that way. I am not sure, though, if the interaction between both interfaces is actually desirable, and if the interaction with VM_SOFTDIRTY is properly taken care of here. soft-dirty is not something that I am particularly exited to see getting used more and in different context. -- Cheers, David / dhildenb