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Message-ID: <20231213072805.74201-1-jianfeng.w.wang@oracle.com>
Date: Tue, 12 Dec 2023 23:28:05 -0800
From: Jianfeng Wang <jianfeng.w.wang@...cle.com>
To: akpm@...ux-foundation.org
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Jianfeng Wang <jianfeng.w.wang@...cle.com>
Subject: [PATCH] mm: remove redundant lru_add_drain() prior to unmapping pages
When unmapping VMA pages, pages will be gathered in batch and released by
tlb_finish_mmu() if CONFIG_MMU_GATHER_NO_GATHER is not set. The function
tlb_finish_mmu() is responsible for calling free_pages_and_swap_cache(),
which calls lru_add_drain() to drain cached pages in folio_batch before
releasing gathered pages. Thus, it is redundant to call lru_add_drain()
before gathering pages, if CONFIG_MMU_GATHER_NO_GATHER is not set.
Remove lru_add_drain() prior to gathering and unmapping pages in
exit_mmap() and unmap_region() if CONFIG_MMU_GATHER_NO_GATHER is not set.
Note that the page unmapping process in oom_killer (e.g., in
__oom_reap_task_mm()) also uses tlb_finish_mmu() and does not have
redundant lru_add_drain(). So, this commit makes the code more consistent.
Signed-off-by: Jianfeng Wang <jianfeng.w.wang@...cle.com>
---
mm/mmap.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/mm/mmap.c b/mm/mmap.c
index 1971bfffcc03..0451285dee4f 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2330,7 +2330,9 @@ static void unmap_region(struct mm_struct *mm, struct ma_state *mas,
struct mmu_gather tlb;
unsigned long mt_start = mas->index;
+#ifdef CONFIG_MMU_GATHER_NO_GATHER
lru_add_drain();
+#endif
tlb_gather_mmu(&tlb, mm);
update_hiwater_rss(mm);
unmap_vmas(&tlb, mas, vma, start, end, tree_end, mm_wr_locked);
@@ -3300,7 +3302,9 @@ void exit_mmap(struct mm_struct *mm)
return;
}
+#ifdef CONFIG_MMU_GATHER_NO_GATHER
lru_add_drain();
+#endif
flush_cache_mm(mm);
tlb_gather_mmu_fullmm(&tlb, mm);
/* update_hiwater_rss(mm) here? but nobody should be looking */
--
2.42.1
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