On Wed, Jul 24, 2024 at 04:13:17PM -0700, Yosry Ahmed wrote:
> On Wed, Jul 24, 2024 at 1:21 PM Roman Gushchin <roman.gushchin@xxxxxxxxx> wrote:
> >
> > Memory protection (min/low) requires a constant tracking of
> > protected memory usage. propagate_protected_usage() is called
> > on each page counters update and does a number of operations
> > even in cases when the actual memory protection functionality
> > is not supported (e.g. hugetlb cgroups or memcg swap counters).
> >
> > It's obviously inefficient and leads to a waste of CPU cycles.
> > It can be addressed by calling propagate_protected_usage() only
> > for the counters which do support memory guarantees. As of now
> > it's only memcg->memory - the unified memory memcg counter.
> >
> > Signed-off-by: Roman Gushchin <roman.gushchin@xxxxxxxxx>
> > ---
> > include/linux/page_counter.h | 8 +++++++-
> > mm/hugetlb_cgroup.c | 4 ++--
> > mm/memcontrol.c | 16 ++++++++--------
> > mm/page_counter.c | 16 +++++++++++++---
> > 4 files changed, 30 insertions(+), 14 deletions(-)
> >
> > diff --git a/include/linux/page_counter.h b/include/linux/page_counter.h
> > index 860f313182e7..b31fd5b208aa 100644
> > --- a/include/linux/page_counter.h
> > +++ b/include/linux/page_counter.h
> > @@ -32,6 +32,7 @@ struct page_counter {
> > /* Keep all the read most fields in a separete cacheline. */
> > CACHELINE_PADDING(_pad2_);
> >
> > + bool protection_support;
> > unsigned long min;
> > unsigned long low;
> > unsigned long high;
> > @@ -45,12 +46,17 @@ struct page_counter {
> > #define PAGE_COUNTER_MAX (LONG_MAX / PAGE_SIZE)
> > #endif
> >
> > +/*
> > + * Protection is supported only for the first counter (with id 0).
> > + */
> > static inline void page_counter_init(struct page_counter *counter,
> > - struct page_counter *parent)
> > + struct page_counter *parent,
> > + bool protection_support)
>
> Would it be better to make this an internal helper (e.g.
> __page_counter_init()), and add another API function that passes in
> protection_support=true, for example:
>
> static inline void page_counter_init_protected(..)
> {
> __page_counter_init(.., true);
> }
>
> This will get rid of the naked booleans at the callsites of
> page_counter_init(), which are more difficult to interpret. It will
> also reduce the diff as we only need to change the page_counter_init()
> calls of memcg->memory.
>
> WDYT?
No strong opinion here. There are basically 2 call sites and I don't expect
this number to grow, so not sure if it makes sense to add 2 new helpers.
Another option I thought about is to leave page_counter_init() as it is
and add a separate function to enable the protection tracking.
Thanks!
