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From: <liuhailong@oppo.com>
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CC: <nathan@kernel.org>, <ndesaulniers@google.com>, <trix@redhat.com>,
	<linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>, <llvm@lists.linux.dev>,
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	<liuhailong@oppo.com>
Subject: [PATCH v2] Revert "mm: skip CMA pages when they are not available"
Date: Fri, 15 Mar 2024 16:18:03 +0800
Message-ID: <20240315081803.2223-1-liuhailong@oppo.com>
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From: "Hailong.Liu" <liuhailong@oppo.com>

This reverts
commit b7108d66318a ("Multi-gen LRU: skip CMA pages when they are not eligible")
commit 5da226dbfce3 ("mm: skip CMA pages when they are not available")

skip_cma may cause system not responding. if cma pages is large in lru_list
and system is in lowmemory, many tasks would direct reclaim and waste
cpu time to isolate_lru_pages and return.

Test this patch on android-5.15 8G device
reproducer:
- cma_declare_contiguous 3G pages
- set /proc/sys/vm/swappiness 0 to enable direct_reclaim reclaim file
  only.
- run a memleak process in userspace

trace the trace_mm_vmscan_lru_isolate which get
[ 1178.059160] 2825  3405 I UsbFfs-worker   : isolate_lru_pages:1895 total_scan: 24385 skipped: 24382
[ 1178.059699] 2825  3405 I UsbFfs-worker   : isolate_lru_pages:1895 total_scan: 24412 skipped: 24401
[ 1178.061747] 2825  3405 I UsbFfs-worker   : isolate_lru_pages:1895 total_scan: 24412 skipped: 24401
From the log, tasks is waste time to scan lru list and call stack as below.

Task name: UsbFfs-worker [affinity: 0xff] pid: 3374 cpu: 7 prio: 120 start: ffffff8897a35c80
state: 0x0[R] exit_state: 0x0 stack base: 0xffffffc01eaa0000
Last_enqueued_ts:       0.000000000 Last_sleep_ts:       0.000000000
Stack:
[<ffffffd32ee7d910>] __switch_to+0x180
[<ffffffd3302022fc>] __schedule+0x4dc
[<ffffffd330201e08>] preempt_schedule+0x5c
[<ffffffd33020a4d0>] _raw_spin_unlock_irq+0x54
[<ffffffd32f14906c>] shrink_inactive_list+0x1d0
[<ffffffd32f143998>] shrink_lruvec+0x1bc
[<ffffffd32f147c0c>] shrink_node_memcgs+0x184
[<ffffffd32f147414>] shrink_node+0x2d0
[<ffffffd32f146d38>] shrink_zones+0x14c
[<ffffffd32f142e84>] do_try_to_free_pages+0xe8
[<ffffffd32f142b08>] try_to_free_pages+0x2e0
[<ffffffd32f1a8e44>] __alloc_pages_direct_reclaim+0x84
[<ffffffd32f1a2d58>] __alloc_pages_slowpath+0x4d0
[<ffffffd32f1a23bc>] __alloc_pages_nodemask[jt]+0x124
[<ffffffd32f19a220>] __vmalloc_area_node+0x188
[<ffffffd32f19a540>] __vmalloc_node+0x148
[<ffffffd32f19a60c>] vmalloc+0x4c
[<ffffffd32f910218>] ffs_epfile_io+0x258
[<ffffffd330033780>] kretprobe_trampoline[jt]+0x0
[<ffffffd330033780>] kretprobe_trampoline[jt]+0x0
[<ffffffd32f28129c>] __io_submit_one+0x1c0
[<ffffffd32f280e38>] io_submit_one+0x88
[<ffffffd32f280c88>] __do_sys_io_submit+0x178
[<ffffffd32f27eac0>] __arm64_sys_io_submit+0x20
[<ffffffd32eeabb74>] el0_svc_common.llvm.9961749221945255377+0xd0
[<ffffffd32eeaba34>] do_el0_svc+0x28
[<ffffffd32ff21be8>] el0_svc+0x14
[<ffffffd32ff21b70>] el0_sync_handler+0x88
[<ffffffd32ee128b8>] el0_sync+0x1b8

Task name: kthreadd [affinity: 0xff] pid: 2 cpu: 7 prio: 120 start: ffffff87808c0000
state: 0x0[R] exit_state: 0x0 stack base: 0xffffffc008078000
Last_enqueued_ts:       0.000000000 Last_sleep_ts:       0.000000000
Stack:
[<ffffffd32ee7d910>] __switch_to+0x180
[<ffffffd3302022fc>] __schedule+0x4dc
[<ffffffd330201e08>] preempt_schedule+0x5c
[<ffffffd33020a4d0>] _raw_spin_unlock_irq+0x54
[<ffffffd32f149168>] shrink_inactive_list+0x2cc
[<ffffffd32f143998>] shrink_lruvec+0x1bc
[<ffffffd32f147c0c>] shrink_node_memcgs+0x184
[<ffffffd32f147414>] shrink_node+0x2d0
[<ffffffd32f146d38>] shrink_zones+0x14c
[<ffffffd32f142e84>] do_try_to_free_pages+0xe8
[<ffffffd32f142b08>] try_to_free_pages+0x2e0
[<ffffffd32f1a8e44>] __alloc_pages_direct_reclaim+0x84
[<ffffffd32f1a2d58>] __alloc_pages_slowpath+0x4d0
[<ffffffd32f1a23bc>] __alloc_pages_nodemask[jt]+0x124
[<ffffffd32f19a220>] __vmalloc_area_node+0x188
[<ffffffd32f19a044>] __vmalloc_node_range+0x88
[<ffffffd32f0fb430>] scs_alloc+0x1b8
[<ffffffd32f0fb62c>] scs_prepare+0x20
[<ffffffd32ef2ce04>] dup_task_struct+0xd4
[<ffffffd32ef2a77c>] copy_process+0x144
[<ffffffd32ef2bae4>] kernel_clone+0xb4
[<ffffffd32ef2c040>] kernel_thread+0x5c
[<ffffffd32ef618d0>] kthreadd+0x184

Signed-off-by: Hailong.Liu <liuhailong@oppo.com>
---
 mm/vmscan.c | 24 ++----------------------
 1 file changed, 2 insertions(+), 22 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 6f13394b112e..29306c29309f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2261,25 +2261,6 @@ static __always_inline void update_lru_sizes(struct lruvec *lruvec,

 }

-#ifdef CONFIG_CMA
-/*
- * It is waste of effort to scan and reclaim CMA pages if it is not available
- * for current allocation context. Kswapd can not be enrolled as it can not
- * distinguish this scenario by using sc->gfp_mask = GFP_KERNEL
- */
-static bool skip_cma(struct folio *folio, struct scan_control *sc)
-{
-	return !current_is_kswapd() &&
-			gfp_migratetype(sc->gfp_mask) != MIGRATE_MOVABLE &&
-			get_pageblock_migratetype(&folio->page) == MIGRATE_CMA;
-}
-#else
-static bool skip_cma(struct folio *folio, struct scan_control *sc)
-{
-	return false;
-}
-#endif
-
 /*
  * Isolating page from the lruvec to fill in @dst list by nr_to_scan times.
  *
@@ -2326,8 +2307,7 @@ static unsigned long isolate_lru_folios(unsigned long nr_to_scan,
 		nr_pages = folio_nr_pages(folio);
 		total_scan += nr_pages;

-		if (folio_zonenum(folio) > sc->reclaim_idx ||
-				skip_cma(folio, sc)) {
+		if (folio_zonenum(folio) > sc->reclaim_idx) {
 			nr_skipped[folio_zonenum(folio)] += nr_pages;
 			move_to = &folios_skipped;
 			goto move;
@@ -4945,7 +4925,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
 	}

 	/* ineligible */
-	if (zone > sc->reclaim_idx || skip_cma(folio, sc)) {
+	if (zone > sc->reclaim_idx) {
 		gen = folio_inc_gen(lruvec, folio, false);
 		list_move_tail(&folio->lru, &lrugen->folios[gen][type][zone]);
 		return true;
--
Changes in v2:
- add reproducer
- fix build error on v6.6-rc7