The patch titled Subject: mm: remove unnecessary calls to lru_add_drain has been added to the -mm mm-unstable branch. Its filename is mm-remove-unnecessary-calls-to-lru_add_drain.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-remove-unnecessary-calls-to-lru_add_drain.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Rik van Riel <riel@xxxxxxxxxxx> Subject: mm: remove unnecessary calls to lru_add_drain Date: Thu, 19 Dec 2024 15:32:53 -0500 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@xxxxxxxxxxx [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@xxxxxxxxxxx> Suggested-by: David Hildenbrand <david@xxxxxxxxxx> Acked-by: Shakeel Butt <shakeel.butt@xxxxxxxxx> Cc: Chris Li <chrisl@xxxxxxxxxx> Cc: David Hildenbrand <david@xxxxxxxxxx> Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Cc: Ryan Roberts <ryan.roberts@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- 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~mm-remove-unnecessary-calls-to-lru_add_drain +++ a/mm/memory.c @@ -2004,7 +2004,6 @@ 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~mm-remove-unnecessary-calls-to-lru_add_drain +++ a/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_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~mm-remove-unnecessary-calls-to-lru_add_drain +++ a/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~mm-remove-unnecessary-calls-to-lru_add_drain +++ a/mm/vma.c @@ -430,7 +430,6 @@ 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, @@ -1132,7 +1131,6 @@ 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, _ Patches currently in -mm which might be from riel@xxxxxxxxxxx are mm-remove-unnecessary-calls-to-lru_add_drain.patch