From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EF67E3093CD for ; Wed, 4 Feb 2026 21:24:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770240241; cv=none; b=gN0i/4gnowTWFoGUOAv0JD5uoEJsaGZS7nUjjBhFC+FcMnD/Wfw3GoMrnOPK/wzOjvTLl2zpYn9WSZzmblQVqS7iNFzEYF/PzYhf/Rs2MrWkIm1GLXSGfPOrVhEpMzIk1bpA897nhm1i7qnC5WOGVMCmC6RjZkyUWIG7oOl8yMk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770240241; c=relaxed/simple; bh=kvt6RfSq5mmKVHA1/fGV6JgGgvGhaQbjcEYu9QCJ8nM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Hq4B/MRVepRksEfmAwaBVdTpIQ9dL6RQWYe0rvUdZKFbQZri5UNyyZc9hSHwQVd0Llq5DFSpbTSllaj1DP0c+CH1HlkMtItxW1SDuGyMro3rfljQNSh7LNUU4Vzhjz5HONEq6Fii+MkHKHU/So9li4/Hg6mb1t2Ko+68389ThzA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=TB/gBxn0; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="TB/gBxn0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CCE01C4CEF7; Wed, 4 Feb 2026 21:23:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770240240; bh=kvt6RfSq5mmKVHA1/fGV6JgGgvGhaQbjcEYu9QCJ8nM=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=TB/gBxn0vfFQQb9YORjszU1lX5IkTjOJ1u3/7THf65vM0u8ZNr0FV57VeiWMStM/y 2YtN6AkLRFjRjW/c+r6hgkgX2JroCZ0CdqdKUjjql+ffDFpo40G8TIwxBIGzFtI60W 7szzPIuh3l/Bdd/mAtprfk8Q2UXb92+6iAs9OLVUg9wGmMTWnmmi/TZWZooZsLcOa7 OyNIpwTRUbbKYMoxw3mF2UjMymhO99IJ3Bok++/fR9erkdPjTTOXhXUAp7y0ix1Mcp OSaiXvkODeedQKWUcj3A1jg8AmfU+PCAnYrGGHSSdAi0AMMl6mLgvpaIPWkFly2MNh xT557Xa8tKrCQ== Message-ID: Date: Wed, 4 Feb 2026 22:23:55 +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 mm-new v6 4/5] mm: khugepaged: skip lazy-free folios To: Vernon Yang , akpm@linux-foundation.org Cc: lorenzo.stoakes@oracle.com, ziy@nvidia.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vernon Yang References: <20260201122554.1470071-1-vernon2gm@gmail.com> <20260201122554.1470071-5-vernon2gm@gmail.com> From: "David Hildenbrand (arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2/1/26 13:25, Vernon Yang wrote: > From: Vernon Yang > > For example, create three task: hot1 -> cold -> hot2. After all three > task are created, each allocate memory 128MB. the hot1/hot2 task > continuously access 128 MB memory, while the cold task only accesses > its memory briefly andthen call madvise(MADV_FREE). However, khugepaged > still prioritizes scanning the cold task and only scans the hot2 task > after completing the scan of the cold task. > > And if we collapse with a lazyfree page, that content will never be none > and the deferred shrinker cannot reclaim them. > > So if the user has explicitly informed us via MADV_FREE that this memory > will be freed, it is appropriate for khugepaged to skip it only, thereby > avoiding unnecessary scan and collapse operations to reducing CPU > wastage. > > Here are the performance test results: > (Throughput bigger is better, other smaller is better) > > Testing on x86_64 machine: > > | task hot2 | without patch | with patch | delta | > |---------------------|---------------|---------------|---------| > | total accesses time | 3.14 sec | 2.93 sec | -6.69% | > | cycles per access | 4.96 | 2.21 | -55.44% | > | Throughput | 104.38 M/sec | 111.89 M/sec | +7.19% | > | dTLB-load-misses | 284814532 | 69597236 | -75.56% | > > Testing on qemu-system-x86_64 -enable-kvm: > > | task hot2 | without patch | with patch | delta | > |---------------------|---------------|---------------|---------| > | total accesses time | 3.35 sec | 2.96 sec | -11.64% | > | cycles per access | 7.29 | 2.07 | -71.60% | > | Throughput | 97.67 M/sec | 110.77 M/sec | +13.41% | > | dTLB-load-misses | 241600871 | 3216108 | -98.67% | > > Signed-off-by: Vernon Yang > --- > include/trace/events/huge_memory.h | 1 + > mm/khugepaged.c | 13 +++++++++++++ > 2 files changed, 14 insertions(+) > > diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h > index 384e29f6bef0..bcdc57eea270 100644 > --- a/include/trace/events/huge_memory.h > +++ b/include/trace/events/huge_memory.h > @@ -25,6 +25,7 @@ > EM( SCAN_PAGE_LRU, "page_not_in_lru") \ > EM( SCAN_PAGE_LOCK, "page_locked") \ > EM( SCAN_PAGE_ANON, "page_not_anon") \ > + EM( SCAN_PAGE_LAZYFREE, "page_lazyfree") \ > EM( SCAN_PAGE_COMPOUND, "page_compound") \ > EM( SCAN_ANY_PROCESS, "no_process_for_page") \ > EM( SCAN_VMA_NULL, "vma_null") \ > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index df22b2274d92..b4def001ccd0 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -46,6 +46,7 @@ enum scan_result { > SCAN_PAGE_LRU, > SCAN_PAGE_LOCK, > SCAN_PAGE_ANON, > + SCAN_PAGE_LAZYFREE, > SCAN_PAGE_COMPOUND, > SCAN_ANY_PROCESS, > SCAN_VMA_NULL, > @@ -583,6 +584,12 @@ static enum scan_result __collapse_huge_page_isolate(struct vm_area_struct *vma, > folio = page_folio(page); > VM_BUG_ON_FOLIO(!folio_test_anon(folio), folio); > > + if (cc->is_khugepaged && !pte_dirty(pteval) && > + folio_test_lazyfree(folio)) { Should be aligned as if (cc->is_khugepaged && !pte_dirty(pteval) && folio_test_lazyfree(folio)) { But you could just have it in a single line. > + result = SCAN_PAGE_LAZYFREE; > + goto out; > + } > + > /* See hpage_collapse_scan_pmd(). */ > if (folio_maybe_mapped_shared(folio)) { > ++shared; > @@ -1332,6 +1339,12 @@ static enum scan_result hpage_collapse_scan_pmd(struct mm_struct *mm, > } > folio = page_folio(page); > > + if (cc->is_khugepaged && !pte_dirty(pteval) && > + folio_test_lazyfree(folio)) { > + result = SCAN_PAGE_LAZYFREE; > + goto out_unmap; > + } Dito. > + > if (!folio_test_anon(folio)) { > result = SCAN_PAGE_ANON; > goto out_unmap; Surprised that there is no need to add checks for SCAN_PAGE_LAZYFREE anywhere, but it's similar to SCAN_PAGE_LOCK just that we cannot ever run into it for madvise. Acked-by: David Hildenbrand (arm) -- Cheers, David