From nobody Mon Feb 9 01:07:50 2026 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CEA55C10F09 for ; Wed, 6 Dec 2023 12:51:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1378197AbjLFMuw (ORCPT ); Wed, 6 Dec 2023 07:50:52 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41474 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1378169AbjLFMuu (ORCPT ); Wed, 6 Dec 2023 07:50:50 -0500 Received: from out0-220.mail.aliyun.com (out0-220.mail.aliyun.com [140.205.0.220]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0BA89D45 for ; Wed, 6 Dec 2023 04:50:53 -0800 (PST) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R211e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018047198;MF=henry.hj@antgroup.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---.Ve5fmIH_1701867051; Received: from localhost(mailfrom:henry.hj@antgroup.com fp:SMTPD_---.Ve5fmIH_1701867051) by smtp.aliyun-inc.com; Wed, 06 Dec 2023 20:50:51 +0800 From: "Henry Huang" To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: "=?UTF-8?B?6LCI6Ym06ZSL?=" , "=?UTF-8?B?5pyx6L6JKOiMtuawtCk=?=" , , "Henry Huang" Subject: [RFC v2] mm: Multi-Gen LRU: fix use mm/page_idle/bitmap Date: Wed, 06 Dec 2023 20:50:07 +0800 Message-ID: <951fb7edab535cf522def4f5f2613947ed7b7d28.1701853894.git.henry.hj@antgroup.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Multi-Gen LRU page-table walker clears pte young flag, but it doesn't clear page idle flag. When we use /sys/kernel/mm/page_idle/bitmap to check whether one page is accessed, it would tell us this page is idle, but actually this page has been accessed. For those unmapped filecache pages, page idle flag would not been cleared in folio_mark_accessed if Multi-Gen LRU is enabled. So we couln't use /sys/kernel/mm/page_idle/bitmap to check whether a filecache page is read or written. What's more, /sys/kernel/mm/page_idle/bitmap also clears pte young flag. If one page is accessed, it would set page young flag. Multi-Gen LRU page-table walker should check both page&pte young flags. how-to-reproduce-problem idle_page_track a tools to track process accessed memory during a specific time usage idle_page_track $pid $time how-it-works 1. scan process vma from /proc/$pid/maps 2. vfn --> pfn from /proc/$pid/pagemap 3. write /sys/kernel/mm/page_idle/bitmap to mark phy page idle flag and clear pte young flag 4. sleep $time 5. read /sys/kernel/mm/page_idle/bitmap to test_and_clear pte young flag and return whether phy page is accessed test ---- test program #include #include #include #include #include #include #include int main(int argc, const char *argv[]) { char *buf =3D NULL; char pipe_info[4096]; int n; int fd =3D -1; buf =3D malloc(1024*1024*1024UL); memset(buf, 0, 1024*1024*1024UL); fd =3D open("access.pipe", O_RDONLY); if (fd < 0) goto out; while (1) { n =3D read(fd, pipe_info, sizeof(pipe_info)); if (!n) { sleep(1); continue; } else if (n < 0) { break; } memset(buf, 0, 1024*1024*1024UL); puts("finish access"); } out: if (fd >=3D0) close(fd); if (buf) free(buf); return 0; } prepare: mkfifo access.pipe ./test ps -ef | grep test root 4106 3148 8 06:47 pts/0 00:00:01 ./test We use /sys/kernel/debug/lru_gen to simulate mglru page-table scan. case 1: mglru walker break page_idle ./idle_page_track 4106 60 & sleep 5; echo 1 > access.pipe sleep 5; echo '+ 8 0 6 1 1' > /sys/kernel/debug/lru_gen the output of idle_page_track is: Est(s) Ref(MB) 64.822 1.00 only found 1MB were accessed during 64.822s, but actually 1024MB were accessed. case 2: page_idle break mglru walker echo 1 > access.pipe ./idle_page_track 4106 10 echo '+ 8 0 7 1 1' > /sys/kernel/debug/lru_gen lru gen status: memcg 8 /user.slice node 0 5 772458 1065 9735 6 737435 262244 72 7 538053 1184 632 8 59404 6422 0 almost pages should be in max_seq-1 queue, but actually not. Signed-off-by: Henry Huang --- mm/swap.c | 3 +++ mm/vmscan.c | 40 ++++++++++++++++++++++++++++------------ 2 files changed, 31 insertions(+), 12 deletions(-) diff --git a/mm/swap.c b/mm/swap.c index cd8f0150ba3a..4bd14aabdc10 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -416,6 +416,9 @@ static void folio_inc_refs(struct folio *folio) { unsigned long new_flags, old_flags =3D READ_ONCE(folio->flags); =20 + if (folio_test_idle(folio)) + folio_clear_idle(folio); + if (folio_test_unevictable(folio)) return; =20 diff --git a/mm/vmscan.c b/mm/vmscan.c index 96abaa5a973e..c1dd9e7bc315 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3297,7 +3297,7 @@ static unsigned long get_pmd_pfn(pmd_t pmd, struct vm= _area_struct *vma, unsigned #endif =20 static struct folio *get_pfn_folio(unsigned long pfn, struct mem_cgroup *m= emcg, - struct pglist_data *pgdat, bool can_swap) + struct pglist_data *pgdat, bool can_swap, bool clear_idle) { struct folio *folio; =20 @@ -3306,6 +3306,10 @@ static struct folio *get_pfn_folio(unsigned long pfn= , struct mem_cgroup *memcg, return NULL; =20 folio =3D pfn_folio(pfn); + + if (clear_idle && folio_test_idle(folio)) + folio_clear_idle(folio); + if (folio_nid(folio) !=3D pgdat->node_id) return NULL; =20 @@ -3355,6 +3359,7 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long = start, unsigned long end, unsigned long pfn; struct folio *folio; pte_t ptent =3D ptep_get(pte + i); + bool is_pte_young; =20 total++; walk->mm_stats[MM_LEAF_TOTAL]++; @@ -3363,16 +3368,20 @@ static bool walk_pte_range(pmd_t *pmd, unsigned lon= g start, unsigned long end, if (pfn =3D=3D -1) continue; =20 - if (!pte_young(ptent)) { - walk->mm_stats[MM_LEAF_OLD]++; + is_pte_young =3D !!pte_young(ptent); + folio =3D get_pfn_folio(pfn, memcg, pgdat, walk->can_swap, is_pte_young); + if (!folio) { + if (!is_pte_young) + walk->mm_stats[MM_LEAF_OLD]++; continue; } =20 - folio =3D get_pfn_folio(pfn, memcg, pgdat, walk->can_swap); - if (!folio) + if (!folio_test_clear_young(folio) && !is_pte_young) { + walk->mm_stats[MM_LEAF_OLD]++; continue; + } =20 - if (!ptep_test_and_clear_young(args->vma, addr, pte + i)) + if (is_pte_young && !ptep_test_and_clear_young(args->vma, addr, pte + i)) VM_WARN_ON_ONCE(true); =20 young++; @@ -3435,6 +3444,7 @@ static void walk_pmd_range_locked(pud_t *pud, unsigne= d long addr, struct vm_area do { unsigned long pfn; struct folio *folio; + bool is_pmd_young; =20 /* don't round down the first address */ addr =3D i ? (*first & PMD_MASK) + i * PMD_SIZE : *first; @@ -3449,11 +3459,15 @@ static void walk_pmd_range_locked(pud_t *pud, unsig= ned long addr, struct vm_area goto next; } =20 - folio =3D get_pfn_folio(pfn, memcg, pgdat, walk->can_swap); + is_pmd_young =3D !!pmd_young(pmd[i]); + folio =3D get_pfn_folio(pfn, memcg, pgdat, walk->can_swap, is_pmd_young); if (!folio) goto next; =20 - if (!pmdp_test_and_clear_young(vma, addr, pmd + i)) + if (is_pmd_young && !pmdp_test_and_clear_young(vma, addr, pmd + i)) + VM_WARN_ON_ONCE(true); + + if (!folio_test_clear_young(folio) && !is_pmd_young) goto next; =20 walk->mm_stats[MM_LEAF_YOUNG]++; @@ -4025,19 +4039,21 @@ void lru_gen_look_around(struct page_vma_mapped_wal= k *pvmw) for (i =3D 0, addr =3D start; addr !=3D end; i++, addr +=3D PAGE_SIZE) { unsigned long pfn; pte_t ptent =3D ptep_get(pte + i); + bool is_pte_young; =20 pfn =3D get_pte_pfn(ptent, pvmw->vma, addr); if (pfn =3D=3D -1) continue; =20 - if (!pte_young(ptent)) + is_pte_young =3D !!pte_young(ptent); + folio =3D get_pfn_folio(pfn, memcg, pgdat, can_swap, is_pte_young); + if (!folio) continue; =20 - folio =3D get_pfn_folio(pfn, memcg, pgdat, can_swap); - if (!folio) + if (!folio_test_clear_young(folio) && !is_pte_young) continue; =20 - if (!ptep_test_and_clear_young(pvmw->vma, addr, pte + i)) + if (is_pte_young && !ptep_test_and_clear_young(pvmw->vma, addr, pte + i)) VM_WARN_ON_ONCE(true); =20 young++; --=20 2.43.0