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SubjectRe: [PATCH V2 3/7] mm: reclaim MADV_FREE pages
On Fri 03-02-17 15:33:19, Shaohua Li wrote:
> When memory pressure is high, we free MADV_FREE pages. If the pages are
> not dirty in pte, the pages could be freed immediately. Otherwise we
> can't reclaim them. We put the pages back to anonumous LRU list (by
> setting SwapBacked flag) and the pages will be reclaimed in normal
> swapout way.
>
> We use normal page reclaim policy. Since MADV_FREE pages are put into
> inactive file list, such pages and inactive file pages are reclaimed
> according to their age. This is expected, because we don't want to
> reclaim too many MADV_FREE pages before used once pages.

Ohh, so this is where the convoluted part sits ;) I thought we just
check for references/dirty bit and make lazy free page regular anon
again and activate it. lazyfree checks in shrink_page_list seem to
be quite excessive to me. Maybe I am just oversimplifying it, though.

> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Shaohua Li <shli@fb.com>
> ---
> mm/rmap.c | 4 ++++
> mm/vmscan.c | 43 +++++++++++++++++++++++++++++++------------
> 2 files changed, 35 insertions(+), 12 deletions(-)
>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index c8d6204..5f05926 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1554,6 +1554,10 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
> dec_mm_counter(mm, MM_ANONPAGES);
> rp->lazyfreed++;
> goto discard;
> + } else if (flags & TTU_LZFREE) {
> + set_pte_at(mm, address, pte, pteval);
> + ret = SWAP_FAIL;
> + goto out_unmap;
> }
>
> if (swap_duplicate(entry) < 0) {
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 947ab6f..b304a84 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -864,7 +864,7 @@ static enum page_references page_check_references(struct page *page,
> return PAGEREF_RECLAIM;
>
> if (referenced_ptes) {
> - if (PageSwapBacked(page))
> + if (PageSwapBacked(page) || PageAnon(page))
> return PAGEREF_ACTIVATE;
> /*
> * All mapped pages start out with page table
> @@ -903,7 +903,7 @@ static enum page_references page_check_references(struct page *page,
>
> /* Check if a page is dirty or under writeback */
> static void page_check_dirty_writeback(struct page *page,
> - bool *dirty, bool *writeback)
> + bool *dirty, bool *writeback, bool lazyfree)
> {
> struct address_space *mapping;
>
> @@ -911,7 +911,7 @@ static void page_check_dirty_writeback(struct page *page,
> * Anonymous pages are not handled by flushers and must be written
> * from reclaim context. Do not stall reclaim based on them
> */
> - if (!page_is_file_cache(page)) {
> + if (!page_is_file_cache(page) || lazyfree) {
> *dirty = false;
> *writeback = false;
> return;
> @@ -971,7 +971,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> int may_enter_fs;
> enum page_references references = PAGEREF_RECLAIM_CLEAN;
> bool dirty, writeback;
> - bool lazyfree = false;
> + bool lazyfree;
> int ret = SWAP_SUCCESS;
>
> cond_resched();
> @@ -986,6 +986,8 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>
> sc->nr_scanned++;
>
> + lazyfree = page_is_lazyfree(page);
> +
> if (unlikely(!page_evictable(page)))
> goto cull_mlocked;
>
> @@ -993,7 +995,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> goto keep_locked;
>
> /* Double the slab pressure for mapped and swapcache pages */
> - if (page_mapped(page) || PageSwapCache(page))
> + if ((page_mapped(page) || PageSwapCache(page)) && !lazyfree)
> sc->nr_scanned++;
>
> may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
> @@ -1005,7 +1007,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> * will stall and start writing pages if the tail of the LRU
> * is all dirty unqueued pages.
> */
> - page_check_dirty_writeback(page, &dirty, &writeback);
> + page_check_dirty_writeback(page, &dirty, &writeback, lazyfree);
> if (dirty || writeback)
> nr_dirty++;
>
> @@ -1107,6 +1109,14 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> ; /* try to reclaim the page below */
> }
>
> + /* lazyfree page could be freed directly */
> + if (lazyfree) {
> + if (unlikely(PageTransHuge(page)) &&
> + split_huge_page_to_list(page, page_list))
> + goto keep_locked;
> + goto unmap_page;
> + }
> +
> /*
> * Anonymous process memory has backing store?
> * Try to allocate it some swap space here.
> @@ -1116,7 +1126,6 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> goto keep_locked;
> if (!add_to_swap(page, page_list))
> goto activate_locked;
> - lazyfree = true;
> may_enter_fs = 1;
>
> /* Adding to swap updated mapping */
> @@ -1128,12 +1137,12 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> }
>
> VM_BUG_ON_PAGE(PageTransHuge(page), page);
> -
> +unmap_page:
> /*
> * The page is mapped into the page tables of one or more
> * processes. Try to unmap it here.
> */
> - if (page_mapped(page) && mapping) {
> + if (page_mapped(page) && (mapping || lazyfree)) {
> switch (ret = try_to_unmap(page, lazyfree ?
> (ttu_flags | TTU_BATCH_FLUSH | TTU_LZFREE) :
> (ttu_flags | TTU_BATCH_FLUSH))) {
> @@ -1145,7 +1154,14 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> case SWAP_MLOCK:
> goto cull_mlocked;
> case SWAP_LZFREE:
> - goto lazyfree;
> + /* follow __remove_mapping for reference */
> + if (page_ref_freeze(page, 1)) {
> + if (!PageDirty(page))
> + goto lazyfree;
> + else
> + page_ref_unfreeze(page, 1);
> + }
> + goto keep_locked;
> case SWAP_SUCCESS:
> ; /* try to free the page below */
> }
> @@ -1257,10 +1273,9 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> }
> }
>
> -lazyfree:
> if (!mapping || !__remove_mapping(mapping, page, true))
> goto keep_locked;
> -
> +lazyfree:
> /*
> * At this point, we have no other references and there is
> * no way to pick any more up (removed from LRU, removed
> @@ -1285,6 +1300,8 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> cull_mlocked:
> if (PageSwapCache(page))
> try_to_free_swap(page);
> + if (lazyfree)
> + SetPageSwapBacked(page);
> unlock_page(page);
> list_add(&page->lru, &ret_pages);
> continue;
> @@ -1294,6 +1311,8 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> if (PageSwapCache(page) && mem_cgroup_swap_full(page))
> try_to_free_swap(page);
> VM_BUG_ON_PAGE(PageActive(page), page);
> + if (lazyfree)
> + SetPageSwapBacked(page);
> SetPageActive(page);
> pgactivate++;
> keep_locked:
> --
> 2.9.3
>

--
Michal Hocko
SUSE Labs

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