On Thu, 14 Apr 2011 15:54:25 -0700
Ying Han <yinghan@xxxxxxxxxx> wrote:
> This is the main loop of per-memcg background reclaim which is implemented in
> function balance_mem_cgroup_pgdat().
>
> The function performs a priority loop similar to global reclaim. During each
> iteration it invokes balance_pgdat_node() for all nodes on the system, which
> is another new function performs background reclaim per node. After reclaiming
> each node, it checks mem_cgroup_watermark_ok() and breaks the priority loop if
> it returns true.
>
> changelog v4..v3:
> 1. split the select_victim_node and zone_unreclaimable to a seperate patches
> 2. remove the logic tries to do zone balancing.
>
> changelog v3..v2:
> 1. change mz->all_unreclaimable to be boolean.
> 2. define ZONE_RECLAIMABLE_RATE macro shared by zone and per-memcg reclaim.
> 3. some more clean-up.
>
> changelog v2..v1:
> 1. move the per-memcg per-zone clear_unreclaimable into uncharge stage.
> 2. shared the kswapd_run/kswapd_stop for per-memcg and global background
> reclaim.
> 3. name the per-memcg memcg as "memcg-id" (css->id). And the global kswapd
> keeps the same name.
> 4. fix a race on kswapd_stop while the per-memcg-per-zone info could be accessed
> after freeing.
> 5. add the fairness in zonelist where memcg remember the last zone reclaimed
> from.
>
> Signed-off-by: Ying Han <yinghan@xxxxxxxxxx>
> ---
> mm/vmscan.c | 161 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 files changed, 161 insertions(+), 0 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 4deb9c8..b8345d2 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -47,6 +47,8 @@
>
> #include <linux/swapops.h>
>
> +#include <linux/res_counter.h>
> +
> #include "internal.h"
>
> #define CREATE_TRACE_POINTS
> @@ -111,6 +113,8 @@ struct scan_control {
> * are scanned.
> */
> nodemask_t *nodemask;
> +
> + int priority;
> };
>
> #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
> @@ -2632,11 +2636,168 @@ static void kswapd_try_to_sleep(struct kswapd *kswapd_p, int order,
> finish_wait(wait_h, &wait);
> }
>
> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR
> +/*
> + * The function is used for per-memcg LRU. It scanns all the zones of the
> + * node and returns the nr_scanned and nr_reclaimed.
> + */
> +static void balance_pgdat_node(pg_data_t *pgdat, int order,
> + struct scan_control *sc)
> +{
> + int i;
> + unsigned long total_scanned = 0;
> + struct mem_cgroup *mem_cont = sc->mem_cgroup;
> + int priority = sc->priority;
> +
> + /*
> + * Now scan the zone in the dma->highmem direction, and we scan
> + * every zones for each node.
> + *
> + * We do this because the page allocator works in the opposite
> + * direction. This prevents the page allocator from allocating
> + * pages behind kswapd's direction of progress, which would
> + * cause too much scanning of the lower zones.
> + */
I guess this comment is a cut-n-paste from global kswapd. It works when
alloc_page() stalls....hmm, I'd like to think whether dma->highmem direction
is good in this case.
As you know, memcg works against user's memory, memory should be in highmem zone.
Memcg-kswapd is not for memory-shortage, but for voluntary page dropping by
_user_.
If this memcg-kswapd drops pages from lower zones first, ah, ok, it's good for
the system because memcg's pages should be on higher zone if we have free memory.
So, I think the reason for dma->highmem is different from global kswapd.
> + for (i = 0; i < pgdat->nr_zones; i++) {
> + struct zone *zone = pgdat->node_zones + i;
> +
> + if (!populated_zone(zone))
> + continue;
> +
> + sc->nr_scanned = 0;
> + shrink_zone(priority, zone, sc);
> + total_scanned += sc->nr_scanned;
> +
> + /*
> + * If we've done a decent amount of scanning and
> + * the reclaim ratio is low, start doing writepage
> + * even in laptop mode
> + */
> + if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
> + total_scanned > sc->nr_reclaimed + sc->nr_reclaimed / 2) {
> + sc->may_writepage = 1;
> + }
> + }
> +
> + sc->nr_scanned = total_scanned;
> + return;
> +}
> +
> +/*
> + * Per cgroup background reclaim.
> + * TODO: Take off the order since memcg always do order 0
> + */
> +static unsigned long balance_mem_cgroup_pgdat(struct mem_cgroup *mem_cont,
> + int order)
> +{
> + int i, nid;
> + int start_node;
> + int priority;
> + bool wmark_ok;
> + int loop;
> + pg_data_t *pgdat;
> + nodemask_t do_nodes;
> + unsigned long total_scanned;
> + struct scan_control sc = {
> + .gfp_mask = GFP_KERNEL,
> + .may_unmap = 1,
> + .may_swap = 1,
> + .nr_to_reclaim = ULONG_MAX,
> + .swappiness = vm_swappiness,
> + .order = order,
> + .mem_cgroup = mem_cont,
> + };
> +
> +loop_again:
> + do_nodes = NODE_MASK_NONE;
> + sc.may_writepage = !laptop_mode;
I think may_writepage should start from '0' always. We're not sure
the system is in memory shortage...we just want to release memory
volunatary. write_page will add huge costs, I guess.
For exmaple,
sc.may_writepage = !!loop
may be better for memcg.
BTW, you set nr_to_reclaim as ULONG_MAX here and doesn't modify it later.
I think you should add some logic to fix it to right value.
For example, before calling shrink_zone(),
sc->nr_to_reclaim = min(SWAP_CLUSETR_MAX, memcg_usage_in_this_zone() / 100); # 1% in this zone.
if we love 'fair pressure for each zone'.
> + sc.nr_reclaimed = 0;
> + total_scanned = 0;
> +
> + for (priority = DEF_PRIORITY; priority >= 0; priority--) {
> + sc.priority = priority;
> + wmark_ok = false;
> + loop = 0;
> +
> + /* The swap token gets in the way of swapout... */
> + if (!priority)
> + disable_swap_token();
> +
> + if (priority == DEF_PRIORITY)
> + do_nodes = node_states[N_ONLINE];
> +
> + while (1) {
> + nid = mem_cgroup_select_victim_node(mem_cont,
> + &do_nodes);
> +
> + /* Indicate we have cycled the nodelist once
> + * TODO: we might add MAX_RECLAIM_LOOP for preventing
> + * kswapd burning cpu cycles.
> + */
> + if (loop == 0) {
> + start_node = nid;
> + loop++;
> + } else if (nid == start_node)
> + break;
> +
> + pgdat = NODE_DATA(nid);
> + balance_pgdat_node(pgdat, order, &sc);
> + total_scanned += sc.nr_scanned;
> +
> + /* Set the node which has at least
> + * one reclaimable zone
> + */
> + for (i = pgdat->nr_zones - 1; i >= 0; i--) {
> + struct zone *zone = pgdat->node_zones + i;
> +
> + if (!populated_zone(zone))
> + continue;
How about checking whether memcg has pages on this node ?
> + }
> + if (i < 0)
> + node_clear(nid, do_nodes);
> +
> + if (mem_cgroup_watermark_ok(mem_cont,
> + CHARGE_WMARK_HIGH)) {
> + wmark_ok = true;
> + goto out;
> + }
> +
> + if (nodes_empty(do_nodes)) {
> + wmark_ok = true;
> + goto out;
> + }
> + }
> +
> + /* All the nodes are unreclaimable, kswapd is done */
> + if (nodes_empty(do_nodes)) {
> + wmark_ok = true;
> + goto out;
> + }
Can this happen ?
> +
> + if (total_scanned && priority < DEF_PRIORITY - 2)
> + congestion_wait(WRITE, HZ/10);
> +
> + if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
> + break;
> + }
> +out:
> + if (!wmark_ok) {
> + cond_resched();
> +
> + try_to_freeze();
> +
> + goto loop_again;
> + }
> +
> + return sc.nr_reclaimed;
> +}
> +#else
> static unsigned long balance_mem_cgroup_pgdat(struct mem_cgroup *mem_cont,
> int order)
> {
> return 0;
> }
> +#endif
>
Thanks,
-Kame
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