From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 11EB23B6C1E; Wed, 26 Aug 2026 09:10:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787735445; cv=none; b=JlIccJGia4Exg5cFGWgU+YRdsWomsKE1SYi9GvU12xdutMBrgvKLtORe0xedVFqMWE7a7xW3h6sZjqB4P0Akk/IklLkxPVx15Og9Joyf1WysJBemj+1+eANfCWp7gXdeMhS+RuZXJW7rntEeGIUSgwCj/kvOkAFsWXHdfV5Ue8w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787735445; c=relaxed/simple; bh=kc1hLDNMDVb37YtbjgdObdlwqpJ+eajUr1evBjwvMaQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=IwJy2ipfEgYvIb45qvVqxrQmolPRJ96MeXAyiu3f4XL/RHHHFf2uDHw77sypKhX46xmBR4eV903Bj1EVopDrmXVTFlYNr4R15bw2TAED6s6Q2xPJguweettvl9D5/evJ+07reORLswVDCW6dnnFCNw6h+412QiQ9jsiqwzA5upI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=S9xyIhYe; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="S9xyIhYe" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 17AA61F000E9; Wed, 26 Aug 2026 09:10:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787735443; bh=j3Se6vqnwz9wr7Aaoob8u5/g7nY4GxqOyEJVx124RT0=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=S9xyIhYe4imNUTEKw6+1shliq7P+QfPGrpzYLo8R2UykC5vV7VVD9WqqJGSdNoDZO m9ODscYqd1hFS5y/w4ef246uekUGi0pR4CBlKTPv64G9R91E0BZr2IVOEUoVJfbKG8 Tm/p/430vyQyn0ZgEeAFiNwaADtzO/JG0D38mXmxU60PLSgCcbcsKh9xk/TATdeFez f6MbiGPTwQhxrJaPQy5JViTs7WIFyfbaqjBcj2XwVSqj7ZT7spEGkHOqGWBfXwk6i3 qC4LWSz6xVmCH8vkhx4iKFbotldMVfe7B806ZQPcno5nCieHUp92Z/mDdSBO3+VES1 2LkR9BmZaGhcg== Message-ID: Date: Wed, 26 Aug 2026 11:10:37 +0200 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 v3 1/3] mm: khugepaged: fix swap entry value to folio_pfn() To: "Lorenzo Stoakes (ARM)" Cc: Vernon Yang , akpm@linux-foundation.org, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, usama.arif@linux.dev, zokeefe@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org, Vernon Yang References: <20260824092935.73892-1-vernon2gm@gmail.com> <20260824092935.73892-2-vernon2gm@gmail.com> <6a9c2369-5589-4f2a-bcfe-c6e3b46a1ccd@gmail.com> <42695df0-3962-4126-9afb-9a1905d096a0@kernel.org> <49aa013f-f613-42be-bc58-35956ef189de@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/26/26 10:35, Lorenzo Stoakes (ARM) wrote: > On Wed, Aug 26, 2026 at 10:24:56AM +0200, David Hildenbrand (Arm) wrote: >> On 8/26/26 10:16, David Hildenbrand (Arm) wrote: >>> >>> Excuse me, what? Are you now just making up arguments? >> To clarify, we have various users of "xxx_pfn" in the tree and I fail to see how >> "this is a problematic pfn" -> "problematic_pfn" is odd and why >> "pfn_problematic" would be any clearer. >> >> I do agree with the "problematic" aspect. "failed" might indeed be nicer. > > Right yeah. Mostly the push back is on the word being a bit confusing. Fair > enough on the pfn thing, failed_pfn is actually the nicest name suggested so far > :) > > I still think: > > if (result == SCAN_SUCCEED) { > ... > trace_mm_khugepaged_scan_file(mm, -1, file, present, swap, result); > } else { > trace_mm_khugepaged_scan_file(mm, failed_pfn, file, present, > swap, result); > } > > Is a little neater as then it's only on the failure path that we trace the > failed pfn, and otherwise we explicitly -1. > > But it's not exactly a show stopper this :) > > Very rough edit of your patch - if you're happy then let's go with this, if not > then edit it + post so Vernon has a clear direction. I'm not feeling super > strongly on this so don't want to block anything: > > ----8<---- > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 75639298efc27..371ee0b16d10c 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2683,6 +2683,7 @@ static enum scan_result collapse_scan_file(struct > mm_struct *mm, > int present, swap; > int node = NUMA_NO_NODE; > enum scan_result result = SCAN_SUCCEED; > + unsigned long failed_pfn = -1; > > present = 0; > swap = 0; > @@ -2714,6 +2715,7 @@ static enum scan_result collapse_scan_file(struct > mm_struct *mm, > } > > if (is_pmd_order(folio_order(folio))) { > + failed_pfn = folio_pfn(folio); > result = SCAN_PTE_MAPPED_HUGEPAGE; > /* > * PMD-sized THP implies that we can only try > @@ -2725,6 +2727,7 @@ static enum scan_result collapse_scan_file(struct > mm_struct *mm, > > node = folio_nid(folio); > if (collapse_scan_abort(node, cc)) { > + failed_pfn = folio_pfn(folio); > result = SCAN_SCAN_ABORT; > folio_put(folio); > break; > @@ -2732,12 +2735,14 @@ static enum scan_result collapse_scan_file(struct > mm_struct *mm, > cc->node_load[node]++; > > if (!folio_test_lru(folio)) { > + failed_pfn = folio_pfn(folio); > result = SCAN_PAGE_LRU; > folio_put(folio); > break; > } > > if (folio_expected_ref_count(folio) + 1 != folio_ref_count(folio)) { > + failed_pfn = folio_pfn(folio); > result = SCAN_PAGE_COUNT; > folio_put(folio); > break; > @@ -2773,7 +2778,7 @@ static enum scan_result collapse_scan_file(struct > mm_struct *mm, > } > - } > - trace_mm_khugepaged_scan_file(mm, folio, file, present, swap, result); > + trace_mm_khugepaged_scan_file(mm, -1, file, present, swap, > + SCAN_SUCCEED); > + } else { > + trace_mm_khugepaged_scan_file(mm, failed_pfn, file, present, > + swap, result); > + } > + > return result; > } That looks good to me, thanks. My memory is bad this week, so I have to ask with the fear of having asked before: is tracing the PFN of any value? What can someone tracing this on userspace reasonably do with the PFN? Inspect kpageflags? I'd assume someone actually doing that is quite ... rare. -- Cheers, David