From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3061ACCD192 for ; Tue, 14 Oct 2025 14:26:34 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 85C2C8E012B; Tue, 14 Oct 2025 10:26:33 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 833F58E010A; Tue, 14 Oct 2025 10:26:33 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 770808E012B; Tue, 14 Oct 2025 10:26:33 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 661608E010A for ; Tue, 14 Oct 2025 10:26:33 -0400 (EDT) Received: from smtpin30.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 260DE5BDDF for ; Tue, 14 Oct 2025 14:26:33 +0000 (UTC) X-FDA: 83996945466.30.C47710F Received: from out-187.mta1.migadu.com (out-187.mta1.migadu.com [95.215.58.187]) by imf07.hostedemail.com (Postfix) with ESMTP id D3EE540009 for ; Tue, 14 Oct 2025 14:26:29 +0000 (UTC) Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=S2d02oP1; spf=pass (imf07.hostedemail.com: domain of lance.yang@linux.dev designates 95.215.58.187 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1760451991; a=rsa-sha256; cv=none; b=Boy/hVLVT4576rKOrOqZ4pZhtuFQLXGTHgB3IlJRSCt3dLRM3HP9is9KVw/VkxHIkw42i7 nNS9ZUZb6L15RNeGB2bBNZL3tPHCaSJeWmb6lo0tnTK9RDAQ9T8l0NrgopwGXzhPExTx7K Xtj7URn6OvE1VzR0q7beLa1Opbm2Oms= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=S2d02oP1; spf=pass (imf07.hostedemail.com: domain of lance.yang@linux.dev designates 95.215.58.187 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1760451991; h=from:from:sender: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:dkim-signature; bh=yKOwPD9G8+OZsBs9+tZFf861qaxj85J1wxUDauqNxYI=; b=tA8Nuv4amQG3MmnKXgRUkiUFWhcxoTWSH4g2LoJvfBZ/IDXl0zBR7nBvdWDj9xepspSFrS lekxRrYwbQ7KQ7XikaHsTO/xeBCjJSHsXvcRIzXkKUx7tjCWvUdxoMM/reUvnjGANRe69E vji/8a/2+5ziS6Z7mcQ56vA5Tr2JhIE= Message-ID: <0bfdbccd-9d4a-409f-ae43-b44bb7347d70@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1760451987; 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=yKOwPD9G8+OZsBs9+tZFf861qaxj85J1wxUDauqNxYI=; b=S2d02oP1UEv0IRpH1hPdj4EYsQk3cuYBa+siMbrG6yg8lsb0Eb54XTRSWFCRjW1mKap5LU Lcj0vNxI9p3glvUB3dU0luEwJyWUrP0wvGsGG/YKJGBq7XeW7N9eZ46svhm166sLw1rVV9 M2GDxG1qcN0Vf8qmrEzHerBdJO7aWc8= Date: Tue, 14 Oct 2025 22:26:20 +0800 MIME-Version: 1.0 Subject: Re: [PATCH mm-new v3 1/1] mm/khugepaged: abort collapse scan on non-swap entries Content-Language: en-US To: Lorenzo Stoakes Cc: akpm@linux-foundation.org, david@redhat.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 References: <20251008032657.72406-1-lance.yang@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Stat-Signature: 8sunxcipokzi31iaic65dbok3oiq9xym X-Rspamd-Queue-Id: D3EE540009 X-Rspamd-Server: rspam09 X-HE-Tag: 1760451989-418726 X-HE-Meta: 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 RlRlRP2m iCubV 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 2025/10/14 19:08, Lorenzo Stoakes wrote: > On Wed, Oct 08, 2025 at 11:26:57AM +0800, Lance Yang wrote: >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index abe54f0043c7..bec3e268dc76 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -1020,6 +1020,11 @@ static int __collapse_huge_page_swapin(struct mm_struct *mm, >> if (!is_swap_pte(vmf.orig_pte)) >> continue; >> >> + if (non_swap_entry(pte_to_swp_entry(vmf.orig_pte))) { >> + result = SCAN_PTE_NON_PRESENT; >> + goto out; >> + } > > OK seems in line with what we were discussing before... Yep. That's the idea :) > >> + >> vmf.pte = pte; >> vmf.ptl = ptl; >> ret = do_swap_page(&vmf); >> @@ -1281,7 +1286,23 @@ 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))) { > Thanks for pointing that out! > Hm but can't this be pte_protnone() at this stage (or something else)? And then Yeah. The funny thing is, a protnone pte cannot actually get here, IIUC. ``` static inline int pte_protnone(pte_t pte) { return (pte_flags(pte) & (_PAGE_PROTNONE | _PAGE_PRESENT)) == _PAGE_PROTNONE; } static inline int pte_present(pte_t a) { return pte_flags(a) & (_PAGE_PRESENT | _PAGE_PROTNONE); } ``` On x86, pte_present() returns true for a protnone pte. And I'd assume other archs behave similarly ... > we're just assuming pte_to_swp_entry() is operating on a swap entry when it in > fact might not be? > > Couldn't we end up with false positives here? Emm, I think we're good here and the code is doing the right thing. > >> + result = SCAN_PTE_NON_PRESENT; >> + goto out_unmap; >> + } >> + >> ++unmapped; >> if (!cc->is_khugepaged || >> unmapped <= khugepaged_max_ptes_swap) { >> @@ -1290,7 +1311,7 @@ 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)) { > > Again you're assuming it's a swap entry but you're not asserting this is a swap > entry in this branch? As we discussed above, the non_swap_entry() check has already kicked out anything that isn't a true swap entry, right? > > Also an aside - I hate, hate, hate how this uffd wp stuff has infiltrated all > kinds of open-coded stuff. It's so gross (not your fault, just a general > comment...) Haha, tell me about it. No argument from me there ;) Thanks, Lance