From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-173.mta1.migadu.com (out-173.mta1.migadu.com [95.215.58.173]) (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 DD319367F3C for ; Tue, 9 Jun 2026 12:04:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781006701; cv=none; b=PQwooPWdpLEHwUYtxDstekX6l7/5pG9p4jwzerAxuH83aUvDQ0JI+RNePc1TUBeun4K50hZcCimP9tyTzuGZrqOo0yPOYHW00TmWFihEJDxp7oa5Ij2tpvInjlomN/t/d+utfVB1ecGp8qnvWHz1EawRQ97WXvkfIXy2Qd1h/XA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781006701; c=relaxed/simple; bh=c8aFJ+oTKb9NTmsARR7cKRPGcFSsJjO9ZqDdrYUqtUU=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=RpfcKkut8tS1bJalOygbKUt8EG+0BWlafz4FVUQR+dMvGqxjQ6AyNj3y1DDncUJ21aHtxEaVuq4Nx1Q7CQfM0pxrwxUJ/bcLaXPMdsqIK++/1k4Cl4NXKLEzjX/YFlHBHDmlj081ldwilFqo2T9HogAbPq1Eooky4cbxqxz7jGs= 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=CXDXQgZI; arc=none smtp.client-ip=95.215.58.173 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="CXDXQgZI" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1781006697; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=k79YIo8QOQKsrDYvlKnWPNsBhiUhq9Oggnh1XXaaAxw=; b=CXDXQgZIWnWZQFuZNeFWGtdtDAqIJpkSM8/sATcbi1GujaaExCPIkUnnO6ZloTfAN/KaQj DoxtVhMY0sY5/G3ZQAabDXlsLPQVqmu1n61wmSwOn7jjH4A44LCSZAAVzGJtuaAjg0Bv9N v8+2eO/Ir0zTJscfgZ1FQD58yxyw7VM= From: Lance Yang To: akpm@linux-foundation.org Cc: david@kernel.org, ljs@kernel.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, liam@infradead.org, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Lance Yang Subject: [PATCH mm-unstable 1/1] mm/khugepaged: fix PMD collapse swap PTE accounting Date: Tue, 9 Jun 2026 20:04:43 +0800 Message-ID: <20260609120443.71864-1-lance.yang@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT From: Lance Yang mthp_collapse() uses mthp_present_ptes to decide whether a range has enough occupied PTEs to try collapse. Swap PTEs accepted by collapse_scan_pmd() are counted in unmapped, but are not represented in mthp_present_ptes. When lower orders are enabled, collapse_scan_pmd() relaxes max_ptes_none so the scan can cover the whole PMD and build the bitmap. mthp_collapse() then checks the PMD-order candidate using the bitmap. With max_ptes_none set to 0, a range with 511 present PTEs and one swap PTE no longer reaches collapse_huge_page(), even though PMD collapse can handle swap PTEs up to max_ptes_swap. Account unmapped PTEs only for PMD order. PMD collapse supports swap PTEs through max_ptes_swap, while lower-order mTHP collapse does not currently support non-present PTEs. Keep non-present PTEs out of the lower-order eligibility check. Signed-off-by: Lance Yang --- Sent separately, as discussed in [1], to spell out the PMD-order swap PTE case. Patch [2] is still only in mm-unstable, so no Fixes: tag. [1] https://lore.kernel.org/linux-mm/CAA1CXcD7WAiA1b9GTLAuNZ+kHaFx0SzZwpBkqAZ=s+RHsTUaow@mail.gmail.com/ [2] https://lore.kernel.org/linux-mm/20260605161422.213817-12-npache@redhat.com/ mm/khugepaged.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index b12187709f6d..617bca76db49 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1508,6 +1508,14 @@ static enum scan_result mthp_collapse(struct mm_struct *mm, nr_occupied_ptes = bitmap_weight_from(cc->mthp_present_ptes, offset, offset + nr_ptes); + /* + * Swap PTEs accepted during the scan are counted in @unmapped, + * not in the present-PTE bitmap. Account them for the PMD-order + * candidate. + */ + if (is_pmd_order(order)) + nr_occupied_ptes += unmapped; + if (nr_occupied_ptes >= nr_ptes - max_ptes_none) { enum scan_result ret; -- 2.49.0