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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768386300; bh=GuHpF+6RmdzfwSAF7TH1se1OHKCtKDO93WP3i/0TrS0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=u7HDROVNmg4kf/SpiPZyAdk0G3o+oWovgIZGE52LqzNXQJo+94l2+faabdjcUbbuO WRFJsce/I32G9huyKT9rZy9ZuZRgUDu1IK/1TjmT0Ye7JkBpCWZM7UR8oD/ayluVqU QQZyGYtpF6Xomrg1T5udaMiQ09QlC8P8Qe7AsBSBT6bJoBdT5I83+mHrxXXPxCu3sF n0Q7vwnQoU6nr0a22PbdDOgWKVsvXqVjxsYC32meVt+p9AQL89N4AbXQW35SQJkXdx Xa7db9GQ3G4fYoXsN/y/Odbkk6ydnH1p7il5P4uKPF2jV/bdyO4bXPkXhP417b8kCi vJNo3UIVTniCg== Message-ID: Date: Wed, 14 Jan 2026 11:24:56 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] ksm: Optimize rmap_walk_ksm by passing a suitable address range To: xu.xin16@zte.com.cn, akpm@linux-foundation.org Cc: chengming.zhou@linux.dev, hughd@google.com, wang.yaxin@zte.com.cn, yang.yang29@zte.com.cn, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Rik van Riel References: <202601141040594302w9Pnbc3vzQLMkh8bQ80D@zte.com.cn> From: "David Hildenbrand (Red Hat)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 95574100006 X-Stat-Signature: hyrd9nxj6fhuyeg7bhmqqwfu4ej7747k X-Rspam-User: X-HE-Tag: 1768386301-830908 X-HE-Meta: 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 +DkHrgHl qnKRXTqFAEJTqsVukNRN0nvtw+sajj7dzhg4bOV79QX+/99FIKtg6ybDgmfOXDRqt7vEyy7OncEXrQILiFUCWg9+Zec3duaB3pE7MKEBG1UuvIYoQxAcPqA1gWBtsYY7z3ShgslRfjpi3D37IduFpvlM2Uiuck3rL0F1PqLdGsVL/9kbj/6fp8IRk52RZX3DA8Xm0QMgEyHc4UOxbMRqsakOqxG2f0HoY7FY4oVnzdjGpfQd0MIhH1jV2ya+jaiBKPTLlD3K7kbTjZA2+OESzShY8mfAIQPPeEgq80crpUkp2pjRsDXnPnBcjDur+ge94TEyqW6xwQBj8B9vJhyjFOjhPB1kegg5Q21TIyEMTSAlTV1k= 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 1/14/26 03:40, xu.xin16@zte.com.cn wrote: >>> Solution >>> ======== >>> In fact, we can significantly improve performance by passing a more precise >>> range based on the given addr. Since the original pages merged by KSM >>> correspond to anonymous VMAs, the page offset can be calculated as >>> pgoff = address >> PAGE_SHIFT. Therefore, we can optimize the call by >>> defining: >>> >>> pgoff_start = rmap_item->address >> PAGE_SHIFT; >>> pgoff_end = pgoff_start + folio_nr_pages(folio) - 1; >>> >>> Performance >>> =========== >>> In our real embedded Linux environment, the measured metrcis were as follows: >>> >>> 1) Time_ms: Max time for holding anon_vma lock in a single rmap_walk_ksm. >>> 2) Nr_iteration_total: The max times of iterations in a loop of anon_vma_interval_tree_foreach >>> 3) Skip_addr_out_of_range: The max times of skipping due to the first check (vma->vm_start >>> and vma->vm_end) in a loop of anon_vma_interval_tree_foreach. >>> 4) Skip_mm_mismatch: The max times of skipping due to the second check (rmap_item->mm == vma->vm_mm) >>> in a loop of anon_vma_interval_tree_foreach. >>> >>> The result is as follows: >>> >>> Time_ms Nr_iteration_total Skip_addr_out_of_range Skip_mm_mismatch >>> Before patched: 228.65 22169 22168 0 >>> After pacthed: 0.396 3 0 2 >> >> Nice improvement. >> >> Can you make your reproducer available? > > I'll do my best to try it. The original test data was derived from real business scenarios, > but it's quite complex. I'll try to simplify this high-latency scenario into a more > understandable demo as a reproduction program. Ah, I thought it was some benchmark ran on an embedded environment. How did you end up measuring these numbers? > >> >>> >>> Co-developed-by: Wang Yaxin >>> Signed-off-by: xu xin >>> --- >>> mm/ksm.c | 6 +++++- >>> 1 file changed, 5 insertions(+), 1 deletion(-) >>> >>> diff --git a/mm/ksm.c b/mm/ksm.c >>> index 335e7151e4a1..0a074ad8e867 100644 >>> --- a/mm/ksm.c >>> +++ b/mm/ksm.c >>> @@ -3172,6 +3172,7 @@ void rmap_walk_ksm(struct folio *folio, struct rmap_walk_control *rwc) >>> struct anon_vma_chain *vmac; >>> struct vm_area_struct *vma; >>> unsigned long addr; >>> + pgoff_t pgoff_start, pgoff_end; >>> >>> cond_resched(); >>> if (!anon_vma_trylock_read(anon_vma)) { >>> @@ -3185,8 +3186,11 @@ void rmap_walk_ksm(struct folio *folio, struct rmap_walk_control *rwc) >>> /* Ignore the stable/unstable/sqnr flags */ >>> addr = rmap_item->address & PAGE_MASK; >>> >>> + pgoff_start = rmap_item->address >> PAGE_SHIFT; >>> + pgoff_end = pgoff_start + folio_nr_pages(folio) - 1; >> >> KSM folios are always order-0, so you can keep it simple and hard-code >> PAGE_SIZE here. >> >> You can also initialize both values directly and make them const. > > Yes, I'll do it in v2. To me, this looks reasonable, but getting some eyes from people more familiar with KSM+interval-tree handling would be great. (CCing also Rik) -- Cheers David