On Wed, Oct 23, 2024 at 2:15 PM Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote: > > 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. +roman.gushchin@xxxxxxxxx CCing Roman's correct email. > > > > > --- > > 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 > > > >
