linux/debian/patches/patchset-pf/invlpgb/0013-mm-remove-unnecessary-calls-to-lru_add_drain.patch

From a3ff46a157cadb29349c5b388fc70804c351e561 Mon Sep 17 00:00:00 2001
From: Rik van Riel <riel@surriel.com>
Date: Thu, 19 Dec 2024 15:32:53 -0500
Subject: 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.

Signed-off-by: Rik van Riel <riel@surriel.com>
Suggested-by: David Hildenbrand <david@redhat.com>
---
 mm/memory.c     | 1 -
 mm/mmap.c       | 2 --
 mm/swap_state.c | 1 -
 mm/vma.c        | 2 --
 4 files changed, 6 deletions(-)

--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1921,7 +1921,6 @@ void zap_page_range_single(struct vm_are
 	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);
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1931,7 +1931,6 @@ 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 */
@@ -2374,7 +2373,6 @@ int relocate_vma_down(struct vm_area_str
 				       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) {
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -317,7 +317,6 @@ void free_pages_and_swap_cache(struct en
 	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]));
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -347,7 +347,6 @@ void unmap_region(struct ma_state *mas,
 	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,
@@ -1089,7 +1088,6 @@ static inline void vms_clear_ptes(struct
 	 * 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,