+ mm-khugepaged-avoid-pointless-allocation-for-struct-mm_slot.patch added to mm-unstable branch

+ mm-khugepaged-avoid-pointless-allocation-for-struct-mm_slot.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm: khugepaged: avoid pointless allocation for "struct mm_slot"
has been added to the -mm mm-unstable branch.  Its filename is
     mm-khugepaged-avoid-pointless-allocation-for-struct-mm_slot.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-khugepaged-avoid-pointless-allocation-for-struct-mm_slot.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Xin Hao <xhao@linux.alibaba.com>
Subject: mm: khugepaged: avoid pointless allocation for "struct mm_slot"
Date: Wed, 31 May 2023 17:58:17 +0800

In __khugepaged_enter(), if "mm->flags" with MMF_VM_HUGEPAGE bit is set,
the "mm_slot" will be released and return, so we can call mm_slot_alloc()
after test_and_set_bit().

Link: https://lkml.kernel.org/r/20230531095817.11012-1-xhao@linux.alibaba.com
Signed-off-by: Xin Hao <xhao@linux.alibaba.com>
Reviewed-by: Andrew Morton <akpm@linux-foudation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/khugepaged.c |   12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

--- a/mm/khugepaged.c~mm-khugepaged-avoid-pointless-allocation-for-struct-mm_slot
+++ a/mm/khugepaged.c
@@ -422,19 +422,17 @@ void __khugepaged_enter(struct mm_struct
 	struct mm_slot *slot;
 	int wakeup;
 
+	/* __khugepaged_exit() must not run from under us */
+	VM_BUG_ON_MM(hpage_collapse_test_exit(mm), mm);
+	if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags)))
+		return;
+
 	mm_slot = mm_slot_alloc(mm_slot_cache);
 	if (!mm_slot)
 		return;
 
 	slot = &mm_slot->slot;
 
-	/* __khugepaged_exit() must not run from under us */
-	VM_BUG_ON_MM(hpage_collapse_test_exit(mm), mm);
-	if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
-		mm_slot_free(mm_slot_cache, mm_slot);
-		return;
-	}
-
 	spin_lock(&khugepaged_mm_lock);
 	mm_slot_insert(mm_slots_hash, mm, slot);
 	/*
_

Patches currently in -mm which might be from xhao@linux.alibaba.com are

mm-khugepaged-avoid-pointless-allocation-for-struct-mm_slot.patch