On Wed 20-05-20 17:31:42, Chris Down wrote:
> Reclaim retries have been set to 5 since the beginning of time in
> 66e1707bc346 ("Memory controller: add per cgroup LRU and reclaim").
> However, we now have a generally agreed-upon standard for page reclaim:
> MAX_RECLAIM_RETRIES (currently 16), added many years later in
> 0a0337e0d1d1 ("mm, oom: rework oom detection").
>
> In the absence of a compelling reason to declare an OOM earlier in memcg
> context than page allocator context, it seems reasonable to supplant
> MEM_CGROUP_RECLAIM_RETRIES with MAX_RECLAIM_RETRIES, making the page
> allocator and memcg internals more similar in semantics when reclaim
> fails to produce results, avoiding premature OOMs or throttling.
>
> Signed-off-by: Chris Down <chris@xxxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
I have already expressed my dislike to some of the MEM_CGROUP_RECLAIM_RETRIES
usage but using MAX_RECLAIM_RETRIES is a reasonable thing to do. There
is simply no reason to have two retry limits.
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> mm/memcontrol.c | 15 ++++++---------
> 1 file changed, 6 insertions(+), 9 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index b040951ccd6b..d3b23c57bed4 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -73,9 +73,6 @@ EXPORT_SYMBOL(memory_cgrp_subsys);
>
> struct mem_cgroup *root_mem_cgroup __read_mostly;
>
> -/* The number of times we should retry reclaim failures before giving up. */
> -#define MEM_CGROUP_RECLAIM_RETRIES 5
> -
> /* Socket memory accounting disabled? */
> static bool cgroup_memory_nosocket;
>
> @@ -2386,7 +2383,7 @@ void mem_cgroup_handle_over_high(void)
> unsigned long pflags;
> unsigned long nr_reclaimed;
> unsigned int nr_pages = current->memcg_nr_pages_over_high;
> - int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> + int nr_retries = MAX_RECLAIM_RETRIES;
> struct mem_cgroup *memcg;
>
> if (likely(!nr_pages))
> @@ -2438,7 +2435,7 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
> unsigned int nr_pages)
> {
> unsigned int batch = max(MEMCG_CHARGE_BATCH, nr_pages);
> - int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> + int nr_retries = MAX_RECLAIM_RETRIES;
> struct mem_cgroup *mem_over_limit;
> struct page_counter *counter;
> unsigned long nr_reclaimed;
> @@ -2557,7 +2554,7 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
> get_order(nr_pages * PAGE_SIZE));
> switch (oom_status) {
> case OOM_SUCCESS:
> - nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> + nr_retries = MAX_RECLAIM_RETRIES;
> goto retry;
> case OOM_FAILED:
> goto force;
> @@ -3168,7 +3165,7 @@ static inline bool memcg_has_children(struct mem_cgroup *memcg)
> */
> static int mem_cgroup_force_empty(struct mem_cgroup *memcg)
> {
> - int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> + int nr_retries = MAX_RECLAIM_RETRIES;
>
> /* we call try-to-free pages for make this cgroup empty */
> lru_add_drain_all();
> @@ -6001,7 +5998,7 @@ static ssize_t memory_high_write(struct kernfs_open_file *of,
> char *buf, size_t nbytes, loff_t off)
> {
> struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
> - unsigned int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> + unsigned int nr_retries = MAX_RECLAIM_RETRIES;
> bool drained = false;
> unsigned long high;
> int err;
> @@ -6049,7 +6046,7 @@ static ssize_t memory_max_write(struct kernfs_open_file *of,
> char *buf, size_t nbytes, loff_t off)
> {
> struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
> - unsigned int nr_reclaims = MEM_CGROUP_RECLAIM_RETRIES;
> + unsigned int nr_reclaims = MAX_RECLAIM_RETRIES;
> bool drained = false;
> unsigned long max;
> int err;
> --
> 2.26.2
--
Michal Hocko
SUSE Labs
