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Date: Wed, 23 Oct 2019 16:14:36 +0200
From: Michal Hocko <mhocko@...nel.org>
To: Johannes Weiner <hannes@...xchg.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel-team@...com
Subject: Re: [PATCH 4/8] mm: vmscan: naming fixes: global_reclaim() and
sane_reclaim()
On Tue 22-10-19 10:47:59, Johannes Weiner wrote:
> Seven years after introducing the global_reclaim() function, I still
> have to double take when reading a callsite. I don't know how others
> do it, this is a terrible name.
I somehow never had problem with that but ...
>
> Invert the meaning and rename it to cgroup_reclaim().
>
> [ After all, "global reclaim" is just regular reclaim invoked from the
> page allocator. It's reclaim on behalf of a cgroup limit that is a
> special case of reclaim, and should be explicit - not the reverse. ]
... this is a valid point.
> sane_reclaim() isn't very descriptive either: it tests whether we can
> use the regular writeback throttling - available during regular page
> reclaim or cgroup2 limit reclaim - or need to use the broken
> wait_on_page_writeback() method. Use "writeback_throttling_sane()".
I do have a stronger opinion on this one. sane_reclaim is really a
terrible name. As you say the only thing this should really tell is
whether writeback throttling is available so I would rather go with
has_writeback_throttling() or writeba_throttling_{eabled,available}
If you insist on having sane in the name then I won't object but it just
raises a question whether we have some levels of throttling with a
different level of sanity.
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
Acked-by: Michal Hocko <mhocko@...e.com>
> ---
> mm/vmscan.c | 38 ++++++++++++++++++--------------------
> 1 file changed, 18 insertions(+), 20 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 622b77488144..302dad112f75 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -239,13 +239,13 @@ static void unregister_memcg_shrinker(struct shrinker *shrinker)
> up_write(&shrinker_rwsem);
> }
>
> -static bool global_reclaim(struct scan_control *sc)
> +static bool cgroup_reclaim(struct scan_control *sc)
> {
> - return !sc->target_mem_cgroup;
> + return sc->target_mem_cgroup;
> }
>
> /**
> - * sane_reclaim - is the usual dirty throttling mechanism operational?
> + * writeback_throttling_sane - is the usual dirty throttling mechanism available?
> * @sc: scan_control in question
> *
> * The normal page dirty throttling mechanism in balance_dirty_pages() is
> @@ -257,11 +257,9 @@ static bool global_reclaim(struct scan_control *sc)
> * This function tests whether the vmscan currently in progress can assume
> * that the normal dirty throttling mechanism is operational.
> */
> -static bool sane_reclaim(struct scan_control *sc)
> +static bool writeback_throttling_sane(struct scan_control *sc)
> {
> - struct mem_cgroup *memcg = sc->target_mem_cgroup;
> -
> - if (!memcg)
> + if (!cgroup_reclaim(sc))
> return true;
> #ifdef CONFIG_CGROUP_WRITEBACK
> if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
> @@ -302,12 +300,12 @@ static void unregister_memcg_shrinker(struct shrinker *shrinker)
> {
> }
>
> -static bool global_reclaim(struct scan_control *sc)
> +static bool cgroup_reclaim(struct scan_control *sc)
> {
> - return true;
> + return false;
> }
>
> -static bool sane_reclaim(struct scan_control *sc)
> +static bool writeback_throttling_sane(struct scan_control *sc)
> {
> return true;
> }
> @@ -1227,7 +1225,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> goto activate_locked;
>
> /* Case 2 above */
> - } else if (sane_reclaim(sc) ||
> + } else if (writeback_throttling_sane(sc) ||
> !PageReclaim(page) || !may_enter_fs) {
> /*
> * This is slightly racy - end_page_writeback()
> @@ -1821,7 +1819,7 @@ static int too_many_isolated(struct pglist_data *pgdat, int file,
> if (current_is_kswapd())
> return 0;
>
> - if (!sane_reclaim(sc))
> + if (!writeback_throttling_sane(sc))
> return 0;
>
> if (file) {
> @@ -1971,7 +1969,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
> reclaim_stat->recent_scanned[file] += nr_taken;
>
> item = current_is_kswapd() ? PGSCAN_KSWAPD : PGSCAN_DIRECT;
> - if (global_reclaim(sc))
> + if (!cgroup_reclaim(sc))
> __count_vm_events(item, nr_scanned);
> __count_memcg_events(lruvec_memcg(lruvec), item, nr_scanned);
> spin_unlock_irq(&pgdat->lru_lock);
> @@ -1985,7 +1983,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
> spin_lock_irq(&pgdat->lru_lock);
>
> item = current_is_kswapd() ? PGSTEAL_KSWAPD : PGSTEAL_DIRECT;
> - if (global_reclaim(sc))
> + if (!cgroup_reclaim(sc))
> __count_vm_events(item, nr_reclaimed);
> __count_memcg_events(lruvec_memcg(lruvec), item, nr_reclaimed);
> reclaim_stat->recent_rotated[0] += stat.nr_activate[0];
> @@ -2309,7 +2307,7 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
> * using the memory controller's swap limit feature would be
> * too expensive.
> */
> - if (!global_reclaim(sc) && !swappiness) {
> + if (cgroup_reclaim(sc) && !swappiness) {
> scan_balance = SCAN_FILE;
> goto out;
> }
> @@ -2333,7 +2331,7 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
> * thrashing file LRU becomes infinitely more attractive than
> * anon pages. Try to detect this based on file LRU size.
> */
> - if (global_reclaim(sc)) {
> + if (!cgroup_reclaim(sc)) {
> unsigned long pgdatfile;
> unsigned long pgdatfree;
> int z;
> @@ -2564,7 +2562,7 @@ static void shrink_node_memcg(struct pglist_data *pgdat, struct mem_cgroup *memc
> * abort proportional reclaim if either the file or anon lru has already
> * dropped to zero at the first pass.
> */
> - scan_adjusted = (global_reclaim(sc) && !current_is_kswapd() &&
> + scan_adjusted = (!cgroup_reclaim(sc) && !current_is_kswapd() &&
> sc->priority == DEF_PRIORITY);
>
> blk_start_plug(&plug);
> @@ -2853,7 +2851,7 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
> * Legacy memcg will stall in page writeback so avoid forcibly
> * stalling in wait_iff_congested().
> */
> - if (!global_reclaim(sc) && sane_reclaim(sc) &&
> + if (cgroup_reclaim(sc) && writeback_throttling_sane(sc) &&
> sc->nr.dirty && sc->nr.dirty == sc->nr.congested)
> set_memcg_congestion(pgdat, root, true);
>
> @@ -2948,7 +2946,7 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
> * Take care memory controller reclaiming has small influence
> * to global LRU.
> */
> - if (global_reclaim(sc)) {
> + if (!cgroup_reclaim(sc)) {
> if (!cpuset_zone_allowed(zone,
> GFP_KERNEL | __GFP_HARDWALL))
> continue;
> @@ -3048,7 +3046,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
> retry:
> delayacct_freepages_start();
>
> - if (global_reclaim(sc))
> + if (!cgroup_reclaim(sc))
> __count_zid_vm_events(ALLOCSTALL, sc->reclaim_idx, 1);
>
> do {
> --
> 2.23.0
--
Michal Hocko
SUSE Labs
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