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 F05DDCD98D5 for ; Fri, 12 Jun 2026 06:46:08 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3B3386B0005; Fri, 12 Jun 2026 02:46:08 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 363156B0088; Fri, 12 Jun 2026 02:46:08 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 252A66B008C; Fri, 12 Jun 2026 02:46:08 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 14F3B6B0005 for ; Fri, 12 Jun 2026 02:46:08 -0400 (EDT) Received: from smtpin21.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay04.hostedemail.com (Postfix) with ESMTP id CBA681A03A5 for ; Fri, 12 Jun 2026 06:46:07 +0000 (UTC) X-FDA: 84870325974.21.356462F Received: from out-181.mta0.migadu.com (out-181.mta0.migadu.com [91.218.175.181]) by imf07.hostedemail.com (Postfix) with ESMTP id E86494000E for ; Fri, 12 Jun 2026 06:46:05 +0000 (UTC) Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=SzWq4ivU; spf=pass (imf07.hostedemail.com: domain of lance.yang@linux.dev designates 91.218.175.181 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=1781246766; 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=tqDd7CCu46FQ8ONM7WEjZvNrKJQRgFQen8hVZWzw+EQ=; b=UuS9r2DBW0KUnZnp65eSOBCSs/jpUE6fze2GMBfGcRy9TdwPjiuSsLQbevH5KUjJyCr2tR YjMqi5Rv9zKBwlLFWECRv6BdbGnDp8nL/N91LkpZ3NYIzlTGDmNUyYtKI1Txg7DgVta2fq KDArhI1OSW6QP+TA7m24O7VLKKENl5Y= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=SzWq4ivU; spf=pass (imf07.hostedemail.com: domain of lance.yang@linux.dev designates 91.218.175.181 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1781246766; b=GBrG6Pq+RQ+j46ZkfoEerb+jtkrjESlDDy3Fd6zTcMV3FIvrcl+zl0cogCrdI2GXqCA6Yu qcQzzuZcD4vrqOhdcdVfRQOWq7jwJjFgcooj4MxBpb5ZuskLIU/cQwC3z39gFyTRB3cuOG BKkGyLEMzuckqoItNRWgmjVI1Ki1Img= 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=1781246761; 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=tqDd7CCu46FQ8ONM7WEjZvNrKJQRgFQen8hVZWzw+EQ=; b=SzWq4ivUXVPN4pB1Cpf3WddSPQPx3UELf13mNC3wAxXbwawJZVYDDZDLu14G7G8JvHS8Lc wZAh4erOzArQKan9EQ6jAcRPJ+0vZTAF4010mx6q08ZlHofVAmaxA+4BcnKo3jeKlnDtvY higrliLn8LnqYupwpUOBVbAgVlYY28I= From: Lance Yang To: usama.arif@linux.dev Cc: akpm@linux-foundation.org, david@kernel.org, chrisl@kernel.org, kasong@tencent.com, ljs@kernel.org, ziy@nvidia.com, ying.huang@linux.alibaba.com, baoquan.he@linux.dev, willy@infradead.org, youngjun.park@lge.com, hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, alex@ghiti.fr, kas@kernel.org, baohua@kernel.org, dev.jain@arm.com, baolin.wang@linux.alibaba.com, npache@redhat.com, liam@infradead.org, ryan.roberts@arm.com, vbabka@kernel.org, lance.yang@linux.dev, linux-kernel@vger.kernel.org, nphamcs@gmail.com, shikemeng@huaweicloud.com, kernel-team@meta.com, linux-mm@kvack.org Subject: Re: [v2 11/16] mm: handle PMD swap entries in non-present PMD walkers Date: Fri, 12 Jun 2026 14:45:50 +0800 Message-Id: <20260612064550.54968-1-lance.yang@linux.dev> In-Reply-To: <20260602142537.198755-12-usama.arif@linux.dev> References: <20260602142537.198755-12-usama.arif@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: E86494000E X-Stat-Signature: nrpsc6msyzbu5panwka5gz9owc9skrpe X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1781246765-808414 X-HE-Meta: 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 Zt7xUK2I 42b0j1ZlNNcsnk4KRlmn9CYz6rvAgNULsOxusgcFYs1xLGdPG/mLKM0To0Ewl8paG2AlFaZ6i/o+SYilrzHnx4bRdWnrV+M29Tb1o/kCRklbygWl7LijfqArUAUZBo1u+tgcVtxBpLOQEzVR7bM2r8CY9UI8g7PcvGc/k1XSbKgdWUib77CXFURhHB4dpuyXnoJqOurf3GMEvNUoLoPqINeMkbg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: +Cc linux-mm Please Cc linux-mm next time. Pretty clearly MM work ... On Tue, Jun 02, 2026 at 07:24:19AM -0700, Usama Arif wrote: [...] >diff --git a/mm/mincore.c b/mm/mincore.c >index e5d13eea9234..3fee8a7b9d9d 100644 >--- a/mm/mincore.c >+++ b/mm/mincore.c >@@ -172,7 +172,19 @@ static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, > > ptl = pmd_trans_huge_lock(pmd, vma); > if (ptl) { >- memset(vec, 1, nr); >+ if (pmd_present(*pmd)) { >+ memset(vec, 1, nr); >+ } else { >+ /* >+ * Non-present PMD: migration, device-private, or PMD >+ * swap entry. Route through mincore_swap() the same way >+ * the PTE path does -- the swap entry covers all 512 >+ * slots, so the whole vec gets the same answer. >+ */ >+ softleaf_t entry = softleaf_from_pmd(*pmd); >+ >+ memset(vec, mincore_swap(entry, false), nr); Looks buggy ... That assumes one swap-cache lookup is enough for whole PMD-sized range. I don't think that always holds ... See do_huge_pmd_swap_page(): ---8<--- folio = swap_cache_get_folio(swp_entry); [...] /* * Folio should be PMD-sized; if not (e.g. split in swap cache), * split the PMD swap entry and retry at PTE level. */ if (folio_nr_pages(folio) != HPAGE_PMD_NR) { folio_unlock(folio); folio_put(folio); goto split_fallback; } --- it handles the case where swap_cache_get_folio() returns a folio that is no longer PMD-sized. E.g. because it was split in the swap cache while the PMD swap entry was installed. Then it split the PMD swap entry and retries at PTE level :) unuse_pmd_entry() has the same fallback. Can mincore hit that case? Maybe the comment right above should say something like: " One lookup is enough for a PMD-sized swapcache folio. If the swapcache was split, check the per-page swap slots. " Hopefully, I'm not missing something here :D Cheers, Lance