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([2804:14c:5fc8:8033:7222:c3bd:a7e0:56ee]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-33fed3db6f7sm112347a91.0.2025.10.24.14.52.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 24 Oct 2025 14:52:16 -0700 (PDT) Message-ID: <51c4dbeb-7df4-458c-bfd1-1744462f50a3@gmail.com> Date: Fri, 24 Oct 2025 18:52:12 -0300 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5] ksm: use range-walk function to jump over holes in scan_get_next_rmap_item To: David Hildenbrand , Andrew Morton Cc: Xu Xin , Chengming Zhou , linux-mm@kvack.org, linux-kernel@vger.kernel.org, craftfever References: <20251023035841.41406-1-pedrodemargomes@gmail.com> Content-Language: en-US From: Pedro Demarchi Gomes In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: A7898100005 X-Stat-Signature: okmi3ct5recdssxjzyxf1xnbhqfwswyj X-Rspam-User: X-HE-Tag: 1761342737-106375 X-HE-Meta: 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 kWGIrYLe 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 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 10/23/25 07:13, David Hildenbrand wrote: > As a note, we have similar code that should probably be doing a range walk instead: unmerge_ksm_pages()->break_ksm(). > > It can be triggered on a range through unmerge_ksm_pages(), which gets called from: > > * ksm_madvise() through madvise(MADV_UNMERGEABLE).  There are not a lot of users of that function. > > * __ksm_del_vma() through ksm_del_vmas(). Effectively called when disabling KSM for a process either through the sysctl or from s390x gmap code when enabling storage keys for a VM. > > In both cases, it's not ksmd that's blocked, it's just that the operation (trigger by the app) takes longer. > > So both are not as critical as this thing here, but likely we should take care of it at some point. > > Interestingly, I converted that from a walk_page_range_vma() to folio_walk_start() after converting it from follow_page() to walk_page_range_vma(). > > But we never did a range walk, we just walked individual addresses, because that's what break_ksm() does. > > We could effectively revert e317a8d8b4f600fc7ec9725e26417030ee594f52 and adjust it to perform an actual range walk by passing a range to break_ksm().  Thanks for letting me know. I will send a patch fixing this issue.