From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-183.mta1.migadu.com (out-183.mta1.migadu.com [95.215.58.183]) (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 4CAFD27E049 for ; Tue, 3 Feb 2026 11:23:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.183 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770117835; cv=none; b=aIGO4mOkrbijHqu7HmNFcYqp1/49djM5+129IYBvkWFQ6SfpW8lqZC44cbrE6akvA2LIoOG8Kd5NM3CsM+I8Tm1wIudiEc6MElmkbEvFFmUl7Y1tgyYcW+bfEWcJDIA0VEb4BCoCLh3M6xHmeHTe+KezoHlGYIYoH7fEHe8fDsM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770117835; c=relaxed/simple; bh=i0GJX7CMi9SjG79c5R3QpXFx1g7GV0+2ZcEjXxaRsZM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=AmQRU/Mj7qxilebfJ9xMex8r377nFG6F7GI91Gm3AvVv2jEwpj7xPtYtsL1epBJ8jOAcbjW7gMyId/eUs1mUpdoYzVMduNPqBuYoxIyHYEJXRL9MowvYofpfho3I6pWplWkFpSMwgDZLTNrxBXgy1NPcGdwWkSonviFVovb8LiM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=wYNSiW0k; arc=none smtp.client-ip=95.215.58.183 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="wYNSiW0k" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1770117831; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Z9CK+57gyxylgnXvGgZfYQ4gb8NRQ2Dah27jPVjSsr8=; b=wYNSiW0kBXQX8yk5biXw6LHBuV/0KwMr2Pj06sAg+HuMQvrtu/cKznpSKwYWvOk/1d+dQd fUqmP+DskKb1Zhw+z6hqs8omWok74WNmVXbOpJpdQqGNY22pTyyJO9iASp2CdGsfTyd7I3 Ack+v+N3Y0KJP+xDcQk5jxPwd5LXlts= Date: Tue, 3 Feb 2026 19:23:39 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH mm-new v6 4/5] mm: khugepaged: skip lazy-free folios Content-Language: en-US To: Vernon Yang Cc: lorenzo.stoakes@oracle.com, ziy@nvidia.com, dev.jain@arm.com, baohua@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vernon Yang , david@kernel.org, akpm@linux-foundation.org References: <20260201122554.1470071-1-vernon2gm@gmail.com> <20260201122554.1470071-5-vernon2gm@gmail.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <20260201122554.1470071-5-vernon2gm@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2026/2/1 20:25, 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 s/andthen/and then/ > 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)) { > + 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; > + } > + > if (!folio_test_anon(folio)) { > result = SCAN_PAGE_ANON; > goto out_unmap; Nothing else jumped at me, LGTM. Reviewed-by: Lance Yang