From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=91.218.175.52 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793904139; b=deE7q4AtFbLJ2Przbv+NKjL5HuqIX8UddPtHJ+6tXXpUdPHvpskGr963tTc+zEXiKTbo x7u+Z8e3lZ1QvCp+Lz973JpHB/uvFM1qOiY6rPTE7KN4UQhgLidVDqMrI2F7/lBcHZqkq 8aAhfy0diOCEA9hkB23ldhCsB4ibh0Y/D76Zl5fzD1R8aNCBKh+/TrWPM6PQlW9y8g+Y7 A4hVZFZVZFFSLRaiOxet8yhjL2j1hNYhRvrtrzAV0QaTAoD48r2cueQ83FjBL8crUp1pP eRUbB6r+GNJW+XIsXhrWlCuez6nbKj2EzhmSfxMk0FvQhMECkXkageOheVwPeorxF9Q== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793904139; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:From:To:Cc:Subject:Date:Message-ID: X-Mailer:In-Reply-To:References:MIME-Version: Content-Transfer-Encoding; bh=KS1pv+WMqgMxUy4k6KpndGUozPH9FDSE1sEg7uWCC1M=; b=ZhczcFPGTm1BlPFnZL1R3wD1T58qRe9LUpl98s5uWE9RUPAIrsoYrBbuHIvnrKz/3Exs VVO6bBOQQKHAyJb3vOEyEqJzrvT1tfYP1q2Z0WWWaFURWFazv5H7DC60HJQNGY1QLVW9f b7Ot0MPVYcMAXpURYr6t7JeZXUY2hjA6enSzlrEPILKYCdpZpxAiBH3vjJ6fpUyjnylCw mwyuCqCSqRbvIOHAMqTK2R9UgK09qxu9CVzAGMn1wcl7Zt7LS0dDAH4w+J+9caI0A5rAc PfRApOvwA8wXa10/kwxxmYjY8W+BJnYDSBxCaMs0ejSj3JNHffYA3MTnAHwDMHisnHw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=tGGPXTJL; arc=none smtp.remote-ip=91.218.175.52 Received: from mta0.migadu.com (out-52.mta0.migadu.com [91.218.175.52]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 90625606A33D for ; Thu, 5 Nov 2026 18:42:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 90625606A33D 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, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=tGGPXTJL X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=GH9JirSt4kIAnAkOjdpYL2+OQteZTYAcIl+OxaWww/s=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793904136; v=1; x=1794508936; b=tGGPXTJLV51YMUD1ZtMIgqEJ0f0S5xTLOcNSK75ai1o7kwv3034Zgzaen611TXIhbc3oFF44 +CzQSpNhbIP5p9AT9EFM5XdpgNunQIoOCGDwe2B5SUwMpnLMC1kBMc44D9uaw5LicJPx9LNvLR0 qkuB3JHyqxs+5DMksjtJ8QbY= X-Envelope-To: linux-kernel@vger.kernel.org Received: by mta12.migadu.com with ESMTPS id 40750e9b963dd24e; Thu, 05 Nov 2026 18:42:16 +0000 X-Mizu-Trace-ID: 40750e9b963dd24e X-Migadu-Flow: FLOW_OUT From: Usama Arif To: Andrew Morton , david@kernel.org, chrisl@kernel.org, kasong@tencent.com, ljs@kernel.org, ziy@nvidia.com, linux-mm@kvack.org Cc: chenhuacai@kernel.org, ying.huang@linux.alibaba.com, Baoquan He , 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, Nico Pache , Liam R. Howlett , ryan.roberts@arm.com, Vlastimil Babka , lance.yang@linux.dev, linux-kernel@vger.kernel.org, nphamcs@gmail.com, shikemeng@huaweicloud.com, yosry@kernel.org, qi.zheng@linux.dev, luizcap@redhat.com, kernel-team@meta.com, Usama Arif Subject: [PATCH v9 27/32] mm: handle PMD swap entries in MADV_WILLNEED Date: Thu, 5 Nov 2026 10:39:11 -0800 Message-ID: <20261105183940.2236717-28-usama.arif@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261105183940.2236717-1-usama.arif@linux.dev> References: <20261105183940.2236717-1-usama.arif@linux.dev> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit swapin_walk_pmd_entry() walks PTEs and cannot descend into a non-present PMD, so MADV_WILLNEED is a no-op on a PMD swap entry. Reading the slots back one at a time would not be much better: order-0 readahead populates per-page swap-cache state, and the fault that follows would then have to split the entry the prefetch was supposed to help. Prefetch the whole range as one PMD-order folio instead, leaving the entry in place so the eventual fault still takes do_huge_pmd_swap_page(). Check the THP policy first: the range was PMD-mapped when it was swapped out, but MADV_NOHUGEPAGE or the sysfs knob may have changed since, and reading at PMD order would then hand do_swap_page() a PMD-sized folio to map with PTEs. A split cache, per-page zswap state, or a failed PMD-order read or allocation falls back to PTEs. Leaving the entry alone would prefetch nothing at all, while the PTE path can still read the slots at order 0. A folio that failed to read is dropped from the swap cache first, so the PTE retry re-reads each slot rather than every later fault returning SIGBUS. Only split if the PMD still looks like the entry that was observed - the decision is taken after the PMD lock has been dropped, so a racing fault may have swapped the range back in as a THP. The test is lockless, so it narrows that window rather than closing it. Signed-off-by: Usama Arif --- mm/madvise.c | 139 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 139 insertions(+) diff --git a/mm/madvise.c b/mm/madvise.c index f7f17efdd926d..576be4b8744c2 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -33,6 +33,7 @@ #include #include #include +#include #include @@ -193,6 +194,108 @@ static int madvise_update_vma(vm_flags_t new_flags, } #ifdef CONFIG_SWAP +/* + * Prefetch a whole PMD swap entry as one PMD-order folio. + * + * Called with the PMD lock held; always drops it. Returns true when the + * caller should ask the walker to retry so the PTE path can handle the + * covered slots individually. + */ +static bool swapin_pmd_swap_entry(struct vm_area_struct *vma, pmd_t *pmd, + unsigned long addr, softleaf_t entry, + spinlock_t *ptl) +{ + struct vm_fault vmf = { + .vma = vma, + .address = addr, + .real_address = addr, + .pmd = pmd, + }; + enum swap_pmd_cache cache_state; + struct swap_info_struct *si; + struct folio *folio; + bool split = false; + + /* + * The range was PMD-mapped when it was swapped out, but the policy may + * have changed since: MADV_NOHUGEPAGE, or the sysfs knob. Reading it + * back at PMD order would then hand do_swap_page() a PMD-sized folio to + * map with PTEs, which is exactly what the policy forbids. Split now + * and let the PTE path prefetch at order 0 - the next fault would split + * the entry anyway, so nothing is lost that the VMA still permits. + */ + if (!thp_vma_allowable_order(vma, vma->vm_flags, TVA_PAGEFAULT, + HPAGE_PMD_ORDER)) { + spin_unlock(ptl); + return true; + } + + cache_state = swap_pmd_cache_lookup(entry, &folio); + if (cache_state == SWAP_PMD_CACHE_HUGE) { + /* Already cached as one PMD-sized folio, nothing to do. */ + folio_put(folio); + spin_unlock(ptl); + return false; + } + if (cache_state == SWAP_PMD_CACHE_SPLIT || + zswap_is_present(entry, HPAGE_PMD_NR)) { + spin_unlock(ptl); + return true; + } + + /* + * Pin the swap device under the PMD lock so the PMD-swap-entry + * observation keeps the entry valid for swapin_sync(). + */ + si = get_swap_device(entry); + spin_unlock(ptl); + if (IS_ERR_OR_NULL(si)) + return false; + + folio = swapin_sync(entry, GFP_HIGHUSER_MOVABLE, BIT(HPAGE_PMD_ORDER), + &vmf, NULL, 0); + + /* + * Fall back to PTE-order swapin: a PMD-order failure does not mean + * that individual slots cannot be read. + */ + if (IS_ERR_OR_NULL(folio)) { + split = true; + goto out; + } + + if (folio_nr_pages(folio) != HPAGE_PMD_NR) { + split = true; + goto out_put; + } + + /* + * A trylock only succeeds once the read has completed, so this never + * blocks MADV_WILLNEED on in-flight I/O. A read that failed - a + * PMD-order zswap load that found per-page state, or an I/O error - + * leaves the folio clean and not uptodate. Drop it from the swap cache + * so the PTE retry reads each slot again; leaving it there would make + * the next fault return VM_FAULT_SIGBUS. Another thread may have + * removed it already, so revalidate the association first. + */ + if (!folio_trylock(folio)) + goto out_put; + + if (!folio_test_uptodate(folio)) { + if (folio_matches_swap_entry(folio, entry)) + swap_cache_del_folio(folio); + split = true; + } + folio_unlock(folio); + +out_put: + folio_put(folio); +out: + /* Keep the device pinned until the last use of @entry. */ + put_swap_device(si); + return split; +} + static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start, unsigned long end, struct mm_walk *walk) { @@ -202,6 +305,41 @@ static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start, spinlock_t *ptl; unsigned long addr; + ptl = pmd_trans_huge_lock(pmd, vma); + if (ptl) { + pmd_t pmdval = *pmd; + + if (pmd_is_swap_entry(pmdval)) { + /* swapin_pmd_swap_entry() always drops the PMD lock. */ + if (!swapin_pmd_swap_entry(vma, pmd, start, + softleaf_from_pmd(pmdval), + ptl)) + goto ret; + /* + * Only split if this still looks like the entry we + * observed. The fallback was decided after the PMD lock + * was dropped, so a racing fault may have swapped the + * range back in as a THP, and splitting that would + * demote a perfectly good huge mapping for an advisory + * hint. The test is lockless, so it narrows that window + * rather than closing it. + */ + if (pmd_same(pmdval, pmdp_get_lockless(pmd))) { + __split_huge_pmd(vma, pmd, start); + walk->action = ACTION_AGAIN; + goto ret; + } + /* + * Somebody else changed the PMD. Leave it alone and let + * the PTE loop below deal with whatever is there now; + * it simply finds no page table if the range came back + * as a THP. + */ + } else { + spin_unlock(ptl); + } + } + for (addr = start; addr < end; addr += PAGE_SIZE) { pte_t pte; softleaf_t entry; @@ -230,6 +368,7 @@ static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start, if (ptep) pte_unmap_unlock(ptep, ptl); swap_read_submit(&ctx); +ret: cond_resched(); return 0; -- 2.53.0-Meta