mm: remove unnecessary calls to lru_add_drain

There seem to be several categories of calls to lru_add_drain and
lru_add_drain_all.

The first are code paths that recently allocated, swapped in, or otherwise
processed a batch of pages, and want them all on the LRU.  These drain
pages that were recently allocated, probably on the local CPU.

A second category are code paths that are actively trying to reclaim,
migrate, or offline memory.  These often use lru_add_drain_all, to drain
the caches on all CPUs.

However, there also seem to be some other callers where we aren't really
doing either.  They are calling lru_add_drain(), despite operating on
pages that may have been allocated long ago, and quite possibly on
different CPUs.

Those calls are not likely to be effective at anything but creating lock
contention on the LRU locks.

Remove the lru_add_drain calls in the latter category.

For detailed reasoning, see [1] and [2].

Link: https://lkml.kernel.org/r/dca2824e8e88e826c6b260a831d79089b5b9c79d.camel@surriel.com [1]
Link: https://lkml.kernel.org/r/xxfhcjaq2xxcl5adastz5omkytenq7izo2e5f4q7e3ns4z6lko@odigjjc7hqrg [2]
Link: https://lkml.kernel.org/r/20241219153253.3da9e8aa@fangorn
Signed-off-by: Rik van Riel <riel@surriel.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

4 files changed, 0 insertions, 6 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 1cee7517d21f..9defa853dbd2 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2004,7 +2004,6 @@ void zap_page_range_single(struct vm_area_struct *vma, unsigned long address,
 	struct mmu_notifier_range range;
 	struct mmu_gather tlb;
 
-	lru_add_drain();
 	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma->vm_mm,
 				address, end);
 	hugetlb_zap_begin(vma, &range.start, &range.end);
diff --git a/mm/mmap.c b/mm/mmap.c
index aef835984b1c..3cc8de07411d 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1336,7 +1336,6 @@ void exit_mmap(struct mm_struct *mm)
 		goto destroy;
 	}
 
-	lru_add_drain();
 	flush_cache_mm(mm);
 	tlb_gather_mmu_fullmm(&tlb, mm);
 	/* update_hiwater_rss(mm) here? but nobody should be looking */
@@ -1779,7 +1778,6 @@ int relocate_vma_down(struct vm_area_struct *vma, unsigned long shift)
 				       vma, new_start, length, false, true))
 		return -ENOMEM;
 
-	lru_add_drain();
 	tlb_gather_mmu(&tlb, mm);
 	next = vma_next(&vmi);
 	if (new_end > old_start) {
diff --git a/mm/swap_state.c b/mm/swap_state.c
index e0c0321b8ff7..ca42b2be64d9 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -317,7 +317,6 @@ void free_pages_and_swap_cache(struct encoded_page **pages, int nr)
 	struct folio_batch folios;
 	unsigned int refs[PAGEVEC_SIZE];
 
-	lru_add_drain();
 	folio_batch_init(&folios);
 	for (int i = 0; i < nr; i++) {
 		struct folio *folio = page_folio(encoded_page_ptr(pages[i]));
diff --git a/mm/vma.c b/mm/vma.c
index 6fa240e5b0c5..0caaeea899a9 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -430,7 +430,6 @@ void unmap_region(struct ma_state *mas, struct vm_area_struct *vma,
 	struct mm_struct *mm = vma->vm_mm;
 	struct mmu_gather tlb;
 
-	lru_add_drain();
 	tlb_gather_mmu(&tlb, mm);
 	update_hiwater_rss(mm);
 	unmap_vmas(&tlb, mas, vma, vma->vm_start, vma->vm_end, vma->vm_end,
@@ -1132,7 +1131,6 @@ static inline void vms_clear_ptes(struct vma_munmap_struct *vms,
 	 * were isolated before we downgraded mmap_lock.
 	 */
 	mas_set(mas_detach, 1);
-	lru_add_drain();
 	tlb_gather_mmu(&tlb, vms->vma->vm_mm);
 	update_hiwater_rss(vms->vma->vm_mm);
 	unmap_vmas(&tlb, mas_detach, vms->vma, vms->start, vms->end,