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    Subject[PATCH] vmscan: memcg needs may_swap (Re: [patch] vmscan: rename sc.may_swap to may_unmap)
    Added
    Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Cc: Balbir Singh <balbir@in.ibm.com>

    I'm sorry for replying to a very old mail.

    > @@ -1713,7 +1713,7 @@ unsigned long try_to_free_mem_cgroup_pag
    > {
    > struct scan_control sc = {
    > .may_writepage = !laptop_mode,
    > - .may_swap = 1,
    > + .may_unmap = 1,
    > .swap_cluster_max = SWAP_CLUSTER_MAX,
    > .swappiness = swappiness,
    > .order = 0,
    > @@ -1723,7 +1723,7 @@ unsigned long try_to_free_mem_cgroup_pag
    > struct zonelist *zonelist;
    >
    > if (noswap)
    > - sc.may_swap = 0;
    > + sc.may_unmap = 0;
    >
    > sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
    > (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
    IIUC, memcg had used may_swap as a flag for "we need to use swap?" as the name indicate.

    Because, when mem+swap hits the limit, trying to swapout pages is meaningless
    as it doesn't change mem+swap usage.

    What do you think of this patch?
    ===
    From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>

    vmscan-rename-scmay_swap-to-may_unmap.patch removed may_swap flag,
    but memcg had used it as a flag for "we need to use swap?", as the
    name indicate.

    And in current implementation, memcg cannot reclaim mapped file caches
    when mem+swap hits the limit.

    re-introduce may_swap flag and handle it at shrink_page_list.

    This patch doesn't influence any scan_control users other than memcg.

    Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
    ---
    mm/vmscan.c | 15 ++++++++++++++-
    1 files changed, 14 insertions(+), 1 deletions(-)

    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index c815653..86118d9 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -64,6 +64,9 @@ struct scan_control {
    /* Can mapped pages be reclaimed? */
    int may_unmap;

    + /* Can pages be swapped as part of reclaim? */
    + int may_swap;
    +
    /* This context's SWAP_CLUSTER_MAX. If freeing memory for
    * suspend, we effectively ignore SWAP_CLUSTER_MAX.
    * In this context, it doesn't matter that we scan the
    @@ -616,6 +619,11 @@ static unsigned long shrink_page_list(struct list_head *page_list,
    if (!sc->may_unmap && page_mapped(page))
    goto keep_locked;

    + if (!sc->may_swap && PageSwapBacked(page)
    + /* SwapCache uses 'swap' already */
    + && !PageSwapCache(page))
    + goto keep_locked;
    +
    /* Double the slab pressure for mapped and swapcache pages */
    if (page_mapped(page) || PageSwapCache(page))
    sc->nr_scanned++;
    @@ -1696,6 +1704,7 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
    .may_writepage = !laptop_mode,
    .swap_cluster_max = SWAP_CLUSTER_MAX,
    .may_unmap = 1,
    + .may_swap = 1,
    .swappiness = vm_swappiness,
    .order = order,
    .mem_cgroup = NULL,
    @@ -1715,6 +1724,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
    struct scan_control sc = {
    .may_writepage = !laptop_mode,
    .may_unmap = 1,
    + .may_swap = 1,
    .swap_cluster_max = SWAP_CLUSTER_MAX,
    .swappiness = swappiness,
    .order = 0,
    @@ -1724,7 +1734,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
    struct zonelist *zonelist;

    if (noswap)
    - sc.may_unmap = 0;
    + sc.may_swap = 0;

    sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
    (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
    @@ -1764,6 +1774,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order)
    struct scan_control sc = {
    .gfp_mask = GFP_KERNEL,
    .may_unmap = 1,
    + .may_swap = 1,
    .swap_cluster_max = SWAP_CLUSTER_MAX,
    .swappiness = vm_swappiness,
    .order = order,
    @@ -2110,6 +2121,7 @@ unsigned long shrink_all_memory(unsigned long nr_pages)
    struct scan_control sc = {
    .gfp_mask = GFP_KERNEL,
    .may_unmap = 0,
    + .may_swap = 1,
    .may_writepage = 1,
    .isolate_pages = isolate_pages_global,
    };
    @@ -2292,6 +2304,7 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
    struct scan_control sc = {
    .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
    .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
    + .may_swap = 1,
    .swap_cluster_max = max_t(unsigned long, nr_pages,
    SWAP_CLUSTER_MAX),
    .gfp_mask = gfp_mask,

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