Hi Joshua, On Wed, Oct 23, 2024 at 1:34 PM Joshua Hahn <joshua.hahnjy@xxxxxxxxx> wrote: > > Changelog > v2: > * Enables the feature only if memcg accounts for hugeTLB usage > * Moves the counter from memcg_stat_item to node_stat_item > * Expands on motivation & justification in commitlog > * Added Suggested-by: Nhat Pham Changelogs usually go at the end, after ---, not as part of the commit log itself. > > This patch introduces a new counter to memory.stat that tracks hugeTLB > usage, only if hugeTLB accounting is done to memory.current. This > feature is enabled the same way hugeTLB accounting is enabled, via > the memory_hugetlb_accounting mount flag for cgroupsv2. > > 1. Why is this patch necessary? > Currently, memcg hugeTLB accounting is an opt-in feature [1] that adds > hugeTLB usage to memory.current. However, the metric is not reported in > memory.stat. Given that users often interpret memory.stat as a breakdown > of the value reported in memory.current, the disparity between the two > reports can be confusing. This patch solves this problem by including > the metric in memory.stat as well, but only if it is also reported in > memory.current (it would also be confusing if the value was reported in > memory.stat, but not in memory.current) > > Aside from the consistentcy between the two files, we also see benefits consistency* > in observability. Userspace might be interested in the hugeTLB footprint > of cgroups for many reasons. For instance, system admins might want to > verify that hugeTLB usage is distributed as expected across tasks: i.e. > memory-intensive tasks are using more hugeTLB pages than tasks that > don't consume a lot of memory, or is seen to fault frequently. Note that are* seen > this is separate from wanting to inspect the distribution for limiting > purposes (in which case, hugeTLB controller makes more sense). > > 2. We already have a hugeTLB controller. Why not use that? > It is true that hugeTLB tracks the exact value that we want. In fact, by > enabling the hugeTLB controller, we get all of the observability > benefits that I mentioned above, and users can check the total hugeTLB > usage, verify if it is distributed as expected, etc. > > With this said, there are 2 problems: > (a) They are still not reported in memory.stat, which means the > disparity between the memcg reports are still there. > (b) We cannot reasonably expect users to enable the hugeTLB controller > just for the sake of hugeTLB usage reporting, especially since > they don't have any use for hugeTLB usage enforcing [2]. > > [1] https://lore.kernel.org/all/20231006184629.155543-1-nphamcs@xxxxxxxxx/ > [2] Of course, we can't make a new patch for every feature that can be > duplicated. However, since the exsting solution of enabling the existing* > hugeTLB controller is an imperfect solution that still leaves a > discrepancy between memory.stat and memory.curent, I think that it > is reasonable to isolate the feature in this case. > > Suggested-by: Nhat Pham <nphamcs@xxxxxxxxx> > Signed-off-by: Joshua Hahn <joshua.hahnjy@xxxxxxxxx> You should also CC linux-mm on such patches. > > --- > include/linux/mmzone.h | 3 +++ > mm/hugetlb.c | 4 ++++ > mm/memcontrol.c | 11 +++++++++++ > mm/vmstat.c | 3 +++ > 4 files changed, 21 insertions(+) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index 17506e4a2835..d3ba49a974b2 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -215,6 +215,9 @@ enum node_stat_item { > #ifdef CONFIG_NUMA_BALANCING > PGPROMOTE_SUCCESS, /* promote successfully */ > PGPROMOTE_CANDIDATE, /* candidate pages to promote */ > +#endif > +#ifdef CONFIG_HUGETLB_PAGE > + HUGETLB_B, Why '_B'? > #endif > /* PGDEMOTE_*: pages demoted */ > PGDEMOTE_KSWAPD, > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 190fa05635f4..055bc91858e4 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -1925,6 +1925,8 @@ void free_huge_folio(struct folio *folio) > pages_per_huge_page(h), folio); > hugetlb_cgroup_uncharge_folio_rsvd(hstate_index(h), > pages_per_huge_page(h), folio); > + if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_HUGETLB_ACCOUNTING) I think we already have a couple of these checks and this patch adds a few more, perhaps we should add a helper at this point to improve readability? Maybe something like memcg_accounts_hugetlb()? > + lruvec_stat_mod_folio(folio, HUGETLB_B, -pages_per_huge_page(h)); > mem_cgroup_uncharge(folio); > if (restore_reserve) > h->resv_huge_pages++; > @@ -3094,6 +3096,8 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, > if (!memcg_charge_ret) > mem_cgroup_commit_charge(folio, memcg); > mem_cgroup_put(memcg); > + if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_HUGETLB_ACCOUNTING) > + lruvec_stat_mod_folio(folio, HUGETLB_B, pages_per_huge_page(h)); > > return folio; > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 7845c64a2c57..de5899eb8203 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -306,6 +306,9 @@ static const unsigned int memcg_node_stat_items[] = { > #endif > #ifdef CONFIG_NUMA_BALANCING > PGPROMOTE_SUCCESS, > +#endif > +#ifdef CONFIG_HUGETLB_PAGE > + HUGETLB_B, > #endif > PGDEMOTE_KSWAPD, > PGDEMOTE_DIRECT, > @@ -1327,6 +1330,9 @@ static const struct memory_stat memory_stats[] = { > #ifdef CONFIG_ZSWAP > { "zswap", MEMCG_ZSWAP_B }, > { "zswapped", MEMCG_ZSWAPPED }, > +#endif > +#ifdef CONFIG_HUGETLB_PAGE > + { "hugeTLB", HUGETLB_B }, nit: I think we usually use lowercase letters when naming stats. > #endif > { "file_mapped", NR_FILE_MAPPED }, > { "file_dirty", NR_FILE_DIRTY }, > @@ -1441,6 +1447,11 @@ static void memcg_stat_format(struct mem_cgroup *memcg, struct seq_buf *s) > for (i = 0; i < ARRAY_SIZE(memory_stats); i++) { > u64 size; > > +#ifdef CONFIG_HUGETLB_PAGE > + if (unlikely(memory_stats[i].idx == HUGETLB_B) && > + !(cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_HUGETLB_ACCOUNTING)) > + continue; > +#endif > size = memcg_page_state_output(memcg, memory_stats[i].idx); > seq_buf_printf(s, "%s %llu\n", memory_stats[i].name, size); > > diff --git a/mm/vmstat.c b/mm/vmstat.c > index b5a4cea423e1..466c40cffeb0 100644 > --- a/mm/vmstat.c > +++ b/mm/vmstat.c > @@ -1269,6 +1269,9 @@ const char * const vmstat_text[] = { > #ifdef CONFIG_NUMA_BALANCING > "pgpromote_success", > "pgpromote_candidate", > +#endif > +#ifdef CONFIG_HUGETLB_PAGE > + "hugeTLB", > #endif > "pgdemote_kswapd", > "pgdemote_direct", > -- > 2.43.5 > >
