On Mon, Jun 03, 2019 at 02:36:55PM +0900, Minchan Kim wrote:
> When a process expects no accesses to a certain memory range
> for a long time, it could hint kernel that the pages can be
> reclaimed instantly but data should be preserved for future use.
> This could reduce workingset eviction so it ends up increasing
> performance.
>
> This patch introduces the new MADV_PAGEOUT hint to madvise(2)
> syscall. MADV_PAGEOUT can be used by a process to mark a memory
> range as not expected to be used for a long time so that kernel
> reclaims *any LRU* pages instantly. The hint can help kernel in deciding
> which pages to evict proactively.
>
> All of error rule is same with MADV_DONTNEED.
>
> Note:
> This hint works with only private pages(IOW, page_mapcount(page) < 2)
> because shared page could have more chance to be accessed from other
> processes sharing the page so that it could cause major fault soon,
> which is inefficient.
>
> * RFC v2
> * make reclaim_pages simple via factoring out isolate logic - hannes
>
> * RFCv1
> * rename from MADV_COLD to MADV_PAGEOUT - hannes
> * bail out if process is being killed - Hillf
> * fix reclaim_pages bugs - Hillf
>
> Signed-off-by: Minchan Kim <minc...@kernel.org>
> ---
> include/linux/swap.h | 1 +
> include/uapi/asm-generic/mman-common.h | 1 +
> mm/madvise.c | 126 +++++++++++++++++++++++++
> mm/vmscan.c | 34 +++++++
> 4 files changed, 162 insertions(+)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 0ce997edb8bb..063c0c1e112b 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -365,6 +365,7 @@ extern int vm_swappiness;
> extern int remove_mapping(struct address_space *mapping, struct page *page);
> extern unsigned long vm_total_pages;
>
> +extern unsigned long reclaim_pages(struct list_head *page_list);
> #ifdef CONFIG_NUMA
> extern int node_reclaim_mode;
> extern int sysctl_min_unmapped_ratio;
> diff --git a/include/uapi/asm-generic/mman-common.h
> b/include/uapi/asm-generic/mman-common.h
> index 1190f4e7f7b9..92e347a89ddc 100644
> --- a/include/uapi/asm-generic/mman-common.h
> +++ b/include/uapi/asm-generic/mman-common.h
> @@ -44,6 +44,7 @@
> #define MADV_WILLNEED 3 /* will need these pages */
> #define MADV_DONTNEED 4 /* don't need these pages */
> #define MADV_COLD 5 /* deactivatie these pages */
> +#define MADV_PAGEOUT 6 /* reclaim these pages */
>
> /* common parameters: try to keep these consistent across architectures */
> #define MADV_FREE 8 /* free pages only if memory pressure */
> diff --git a/mm/madvise.c b/mm/madvise.c
> index ab158766858a..b010249cb8b6 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -41,6 +41,7 @@ static int madvise_need_mmap_write(int behavior)
> case MADV_WILLNEED:
> case MADV_DONTNEED:
> case MADV_COLD:
> + case MADV_PAGEOUT:
> case MADV_FREE:
> return 0;
> default:
> @@ -415,6 +416,128 @@ static long madvise_cold(struct vm_area_struct *vma,
> return 0;
> }
>
> +static int madvise_pageout_pte_range(pmd_t *pmd, unsigned long addr,
> + unsigned long end, struct mm_walk *walk)
> +{
> + pte_t *orig_pte, *pte, ptent;
> + spinlock_t *ptl;
> + LIST_HEAD(page_list);
> + struct page *page;
> + int isolated = 0;
> + struct vm_area_struct *vma = walk->vma;
> + unsigned long next;
> +
> + if (fatal_signal_pending(current))
> + return -EINTR;
> +
> + next = pmd_addr_end(addr, end);
> + if (pmd_trans_huge(*pmd)) {
> + ptl = pmd_trans_huge_lock(pmd, vma);
> + if (!ptl)
> + return 0;
> +
> + if (is_huge_zero_pmd(*pmd))
> + goto huge_unlock;
> +
> + page = pmd_page(*pmd);
> + if (page_mapcount(page) > 1)
> + goto huge_unlock;
> +
> + if (next - addr != HPAGE_PMD_SIZE) {
> + int err;
> +
> + get_page(page);
> + spin_unlock(ptl);
> + lock_page(page);
> + err = split_huge_page(page);
> + unlock_page(page);
> + put_page(page);
> + if (!err)
> + goto regular_page;
> + return 0;
> + }
> +
> + if (isolate_lru_page(page))
> + goto huge_unlock;
> +
> + list_add(&page->lru, &page_list);
> +huge_unlock:
> + spin_unlock(ptl);
> + reclaim_pages(&page_list);
> + return 0;
> + }
> +
> + if (pmd_trans_unstable(pmd))
> + return 0;
> +regular_page:
> + orig_pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> + for (pte = orig_pte; addr < end; pte++, addr += PAGE_SIZE) {
> + ptent = *pte;
> + if (!pte_present(ptent))
> + continue;
> +
> + page = vm_normal_page(vma, addr, ptent);
> + if (!page)
> + continue;
> +
> + if (page_mapcount(page) > 1)
> + continue;
> +
> + if (isolate_lru_page(page))
> + continue;
> +
> + isolated++;
> + list_add(&page->lru, &page_list);
> + if (isolated >= SWAP_CLUSTER_MAX) {
> + pte_unmap_unlock(orig_pte, ptl);
> + reclaim_pages(&page_list);
> + isolated = 0;
> + pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> + orig_pte = pte;
> + }
> + }
> +
> + pte_unmap_unlock(orig_pte, ptl);
> + reclaim_pages(&page_list);
> + cond_resched();
> +
> + return 0;
> +}
> +
> +static void madvise_pageout_page_range(struct mmu_gather *tlb,
> + struct vm_area_struct *vma,
> + unsigned long addr, unsigned long end)
> +{
> + struct mm_walk warm_walk = {
> + .pmd_entry = madvise_pageout_pte_range,
> + .mm = vma->vm_mm,
> + };
> +
> + tlb_start_vma(tlb, vma);
> + walk_page_range(addr, end, &warm_walk);
> + tlb_end_vma(tlb, vma);
> +}
> +
> +
> +static long madvise_pageout(struct vm_area_struct *vma,
> + struct vm_area_struct **prev,
> + unsigned long start_addr, unsigned long end_addr)
> +{
> + struct mm_struct *mm = vma->vm_mm;
> + struct mmu_gather tlb;
> +
> + *prev = vma;
> + if (!can_madv_lru_vma(vma))
> + return -EINVAL;
> +
> + lru_add_drain();
> + tlb_gather_mmu(&tlb, mm, start_addr, end_addr);
> + madvise_pageout_page_range(&tlb, vma, start_addr, end_addr);
> + tlb_finish_mmu(&tlb, start_addr, end_addr);
> +
> + return 0;
> +}
> +
> static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
> unsigned long end, struct mm_walk *walk)
>
> @@ -805,6 +928,8 @@ madvise_vma(struct vm_area_struct *vma, struct
> vm_area_struct **prev,
> return madvise_willneed(vma, prev, start, end);
> case MADV_COLD:
> return madvise_cold(vma, prev, start, end);
> + case MADV_PAGEOUT:
> + return madvise_pageout(vma, prev, start, end);
> case MADV_FREE:
> case MADV_DONTNEED:
> return madvise_dontneed_free(vma, prev, start, end, behavior);
> @@ -827,6 +952,7 @@ madvise_behavior_valid(int behavior)
> case MADV_DONTNEED:
> case MADV_FREE:
> case MADV_COLD:
> + case MADV_PAGEOUT:
> #ifdef CONFIG_KSM
> case MADV_MERGEABLE:
> case MADV_UNMERGEABLE:
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 56df55e8afcd..2c2cf442db58 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2136,6 +2136,40 @@ static void shrink_active_list(unsigned long
> nr_to_scan,
> nr_deactivate, nr_rotated, sc->priority, file);
> }
>
> +unsigned long reclaim_pages(struct list_head *page_list)
> +{
> + unsigned long nr_reclaimed = 0;
> + LIST_HEAD(node_page_list);
> + struct reclaim_stat dummy_stat;
> + struct scan_control sc = {
> + .gfp_mask = GFP_KERNEL,
> + .priority = DEF_PRIORITY,
> + .may_writepage = 1,
> + .may_unmap = 1,
> + .may_swap = 1,
> + };
> +
> + while (!list_empty(page_list)) {
> + struct page *page;
> +
> + page = lru_to_page(page_list);
> + list_move(&page->lru, &node_page_list);
> + nr_reclaimed += shrink_page_list(&node_page_list,
> + page_pgdat(page),
> + &sc, TTU_IGNORE_ACCESS,
> + &dummy_stat, true);
> + if (!list_empty(&node_page_list)) {
> + struct page *page = lru_to_page(&node_page_list);
> +
> + list_del(&page->lru);
> + putback_lru_page(page);
> +
> + }
> + }
Awesome, this is way more readable now. Thanks for the cleanup!
Regarding the loop, for the vast majority of instances, pages on
page_list will actually be from the same node. It would make sense to
do batching here and collect pages until last_pgdat != pgdat. That
should reduce the number of tlb flushes and memcg uncharge flushes in
shrink_page_list().
