On Wed, Feb 22, 2017 at 10:50:42AM -0800, 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.
>
> Based on Minchan's original patch
>
> Cc: Michal Hocko <mho...@suse.com>
> Cc: Minchan Kim <minc...@kernel.org>
> Cc: Hugh Dickins <hu...@google.com>
> Cc: Johannes Weiner <han...@cmpxchg.org>
> Cc: Rik van Riel <r...@redhat.com>
> Cc: Mel Gorman <mgor...@techsingularity.net>
> Cc: Andrew Morton <a...@linux-foundation.org>
> Signed-off-by: Shaohua Li <s...@fb.com>
> ---
> include/linux/rmap.h | 2 +-
> mm/huge_memory.c | 2 ++
> mm/madvise.c | 1 +
> mm/rmap.c | 10 ++++++++--
> mm/vmscan.c | 34 ++++++++++++++++++++++------------
> 5 files changed, 34 insertions(+), 15 deletions(-)
>
> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> index e2cd8f9..2bfd8c6 100644
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -300,6 +300,6 @@ static inline int page_mkclean(struct page *page)
> #define SWAP_AGAIN 1
> #define SWAP_FAIL 2
> #define SWAP_MLOCK 3
> -#define SWAP_LZFREE 4
> +#define SWAP_DIRTY 4
Could you write down about SWAP_DIRTY in try_to_unmap's description?
< snip >
> diff --git a/mm/rmap.c b/mm/rmap.c
> index c621088..083f32e 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1424,6 +1424,12 @@ 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 (!PageSwapBacked(page)) {
> + /* dirty MADV_FREE page */
> + set_pte_at(mm, address, pvmw.pte, pteval);
> + ret = SWAP_DIRTY;
> + page_vma_mapped_walk_done(&pvmw);
> + break;
> }
>
> if (swap_duplicate(entry) < 0) {
> @@ -1525,8 +1531,8 @@ int try_to_unmap(struct page *page, enum ttu_flags
> flags)
>
> if (ret != SWAP_MLOCK && !page_mapcount(page)) {
> ret = SWAP_SUCCESS;
> - if (rp.lazyfreed && !PageDirty(page))
> - ret = SWAP_LZFREE;
> + if (rp.lazyfreed && PageDirty(page))
> + ret = SWAP_DIRTY;
Hmm, I don't understand why we need to introduce new return value.
Can't we set SetPageSwapBacked and return SWAP_FAIL in try_to_unmap_one?
> }
> return ret;
> }
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 68ea50d..830981a 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
< snip >
> goto keep_locked;
>
> /* Double the slab pressure for mapped and swapcache pages */
> - if (page_mapped(page) || PageSwapCache(page))
> + if ((page_mapped(page) || PageSwapCache(page)) &&
> + !(PageAnon(page) && !PageSwapBacked(page)))
> sc->nr_scanned++;
>
> may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
> @@ -1118,8 +1120,10 @@ static unsigned long shrink_page_list(struct list_head
> *page_list,
> /*
> * Anonymous process memory has backing store?
> * Try to allocate it some swap space here.
> + * Lazyfree page could be freed directly
> */
> - if (PageAnon(page) && !PageSwapCache(page)) {
> + if (PageAnon(page) && !PageSwapCache(page) &&
> + PageSwapBacked(page)) {
> if (!(sc->gfp_mask & __GFP_IO))
> goto keep_locked;
> if (!add_to_swap(page, page_list))
> @@ -1140,9 +1144,12 @@ static unsigned long shrink_page_list(struct list_head
> *page_list,
> * 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)) {
> switch (ret = try_to_unmap(page,
> ttu_flags | TTU_BATCH_FLUSH)) {
> + case SWAP_DIRTY:
> + SetPageSwapBacked(page);
> + /* fall through */
> case SWAP_FAIL:
> nr_unmap_fail++;
> goto activate_locked;
