From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-188.mta0.migadu.com (out-188.mta0.migadu.com [91.218.175.188]) (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 46D9E2D0283 for ; Mon, 29 Sep 2025 10:10:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759140627; cv=none; b=P4YYWtvcBPRRRXSJOTd4ahMMfGqLhMHj7QBL18Re0o2o8KYPJyYxoy47jA2VAWrmxCGhn+slvAuYuhdAK1ZtnslxeDgCW7oLoR52GctfXBLwgudPglvLsQmqB0UDQJWkkHh2ELjbbnGkvf3rfaIPVleVkhWpKUbrUxKj7doR4Fk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759140627; c=relaxed/simple; bh=/Qj6ybaf/hGcvP4WosxlRa1GS7TmZWBfrwTpgHrqB3o=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=j6DezCyL78Yml7w6uGtWkqGnfMqJ3D5T/qPTjeGokV6JntD8zkFseu6ixkJi+7x/U3peFZnhi/G+uZA7lHV0K28s0nJWB6EJA4x034maVBioyTObKc4ncImH0Wl+yWgi1oxTyPEbVPHLEG8g2gLgRplHe19db04RhWXXOBd0fL8= 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=ZLIgf0R2; arc=none smtp.client-ip=91.218.175.188 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="ZLIgf0R2" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1759140623; 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=rV9QK51rsx4eLWCMpcFHElTpfQGO2X4unrpezssK7M4=; b=ZLIgf0R2iCYlSrfsjOq/7WtFyFLGOg/YA6lT0DXwDmN/8fZktfpgKoMqf9JmwBwFzqUmGM SPwbJ2r19RNrqWXAn2BReT26CAYlM6ZiSrGo3pztvreXdbnecNuoeLH/OL3mLrkgqsLZRQ G8kDE47McoqbJdkRDKB1ELIhptJl4k8= Date: Mon, 29 Sep 2025 18:10:10 +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 1/1] mm/khugepaged: abort collapse scan on non-swap entries Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang To: David Hildenbrand Cc: lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, dev.jain@arm.com, hughd@google.com, ioworker0@gmail.com, kirill@shutemov.name, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mpenttil@redhat.com, npache@redhat.com, ryan.roberts@arm.com, ziy@nvidia.com, richard.weiyang@gmail.com, akpm@linux-foundation.org References: <20250924100207.28332-1-lance.yang@linux.dev> <1282de5a-3dce-443d-91d1-111103140973@redhat.com> <69621b58-5142-48ea-9dd8-6baed69e50f8@linux.dev> In-Reply-To: <69621b58-5142-48ea-9dd8-6baed69e50f8@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 2025/9/24 19:47, Lance Yang wrote: > > > On 2025/9/24 18:10, David Hildenbrand wrote: >> On 24.09.25 12:02, Lance Yang wrote: >>> From: Lance Yang >>> >>> The existing check in hpage_collapse_scan_pmd() is specific to uffd-wp >>> markers. Other special markers (e.g., GUARD, POISONED) would not be >>> caught >>> early, leading to failures deeper in the swap-in logic. >>> >>> hpage_collapse_scan_pmd() >>>   `- collapse_huge_page() >>>       `- __collapse_huge_page_swapin() -> fails! >>> >>> As David suggested[1], this patch skips any such non-swap entries early. >>> If a special marker is found, the scan is aborted immediately with the >>> SCAN_PTE_NON_PRESENT result, as Lorenzo suggested[2], avoiding wasted >>> work. >> >> Note that I suggested to skip all non-present entries except swap >> entries, which includes migration entries, hwpoisoned entries etc. > > Oops, I completely misunderstood your suggestion :( > > It should be to handle all special non-present entries (migration, > hwpoison, markers), not just a specific type of marker ... > > How about this version, which handles all non-swap entries as you > suggested? @David Gently ping ... > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 7ab2d1a42df3..27f432e7f07c 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -1284,7 +1284,23 @@ static int hpage_collapse_scan_pmd(struct > mm_struct *mm, >         for (addr = start_addr, _pte = pte; _pte < pte + HPAGE_PMD_NR; >              _pte++, addr += PAGE_SIZE) { >                 pte_t pteval = ptep_get(_pte); > -               if (is_swap_pte(pteval)) { > +               if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { > +                       ++none_or_zero; > +                       if (!userfaultfd_armed(vma) && > +                           (!cc->is_khugepaged || > +                            none_or_zero <= khugepaged_max_ptes_none)) { > +                               continue; > +                       } else { > +                               result = SCAN_EXCEED_NONE_PTE; > +                               count_vm_event(THP_SCAN_EXCEED_NONE_PTE); > +                               goto out_unmap; > +                       } > +               } else if (!pte_present(pteval)) { > +                       if (non_swap_entry(pte_to_swp_entry(pteval))) { > +                               result = SCAN_PTE_NON_PRESENT; > +                               goto out_unmap; > +                       } > + >                         ++unmapped; >                         if (!cc->is_khugepaged || >                             unmapped <= khugepaged_max_ptes_swap) { > @@ -1293,7 +1309,7 @@ static int hpage_collapse_scan_pmd(struct > mm_struct *mm, >                                  * enabled swap entries.  Please see >                                  * comment below for pte_uffd_wp(). >                                  */ > -                               if (pte_swp_uffd_wp_any(pteval)) { > +                               if (pte_swp_uffd_wp(pteval)) { >                                         result = SCAN_PTE_UFFD_WP; >                                         goto out_unmap; >                                 } > @@ -1304,18 +1320,6 @@ static int hpage_collapse_scan_pmd(struct > mm_struct *mm, >                                 goto out_unmap; >                         } >                 } > -               if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { > -                       ++none_or_zero; > -                       if (!userfaultfd_armed(vma) && > -                           (!cc->is_khugepaged || > -                            none_or_zero <= khugepaged_max_ptes_none)) { > -                               continue; > -                       } else { > -                               result = SCAN_EXCEED_NONE_PTE; > -                               count_vm_event(THP_SCAN_EXCEED_NONE_PTE); > -                               goto out_unmap; > -                       } > -               } >                 if (pte_uffd_wp(pteval)) { >                         /* >                          * Don't collapse the page if any of the small > --- > > Thanks, > Lance