Re: [PATCH v2] mm: add per-order mTHP alloc_success and alloc_fail counters

[Barry Song <21cnbao@gmail.com>]

On Wed, Apr 3, 2024 at 7:46 AM David Hildenbrand <david@redhat.com> wrote:
>
> On 28.03.24 10:51, Barry Song wrote:
> > From: Barry Song <v-songbaohua@oppo.com>
> >
> > Profiling a system blindly with mTHP has become challenging due
> > to the lack of visibility into its operations. Presenting the
> > success rate of mTHP allocations appears to be pressing need.
> >
> > Recently, I've been experiencing significant difficulty debugging
> > performance improvements and regressions without these figures.
> > It's crucial for us to understand the true effectiveness of
> > mTHP in real-world scenarios, especially in systems with
> > fragmented memory.
> >
> > This patch sets up the framework for per-order mTHP counters,
> > starting with the introduction of alloc_success and alloc_fail
> > counters.  Incorporating additional counters should now be
> > straightforward as well.
> >
> > The initial two unsigned longs for each event are unused, given
> > that order-0 and order-1 are not mTHP. Nonetheless, this refinement
> > improves code clarity.
> >
> > Signed-off-by: Barry Song <v-songbaohua@oppo.com>
> > ---
> >   -v2:
> >   * move to sysfs and provide per-order counters; David, Ryan, Willy
> >   -v1:
> >   https://lore.kernel.org/linux-mm/20240326030103.50678-1-21cnbao@gmail.com/
> >
> >   include/linux/huge_mm.h | 17 +++++++++++++
> >   mm/huge_memory.c        | 54 +++++++++++++++++++++++++++++++++++++++++
> >   mm/memory.c             |  3 +++
> >   3 files changed, 74 insertions(+)
> >
> > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> > index e896ca4760f6..27fa26a22a8f 100644
> > --- a/include/linux/huge_mm.h
> > +++ b/include/linux/huge_mm.h
> > @@ -264,6 +264,23 @@ unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
> >                                         enforce_sysfs, orders);
> >   }
> >
> > +enum thp_event_item {
> > +     THP_ALLOC_SUCCESS,
> > +     THP_ALLOC_FAIL,
> > +     NR_THP_EVENT_ITEMS
> > +};
>
> I'm wondering if these should be ANON specific for now. We might want to
> add others (shmem, file) in the future.

I've two ways to do that
1. rename to ANON_THP_ALLOC, so that I can have SHMEM_THP_ALLOC, FILE_THP_ALLOC
in the future;
2. let THP_ALLOC cover all of shmem, file and anon.

following vmstat, actually 1 might be better as we have both THP_FAULT_ALLOC and
THP_FILE_ALLOC for pmd-mapped THP.

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
                THP_FAULT_ALLOC,
                THP_FAULT_FALLBACK,
                THP_FAULT_FALLBACK_CHARGE,
                THP_COLLAPSE_ALLOC,
                THP_COLLAPSE_ALLOC_FAILED,
                THP_FILE_ALLOC,
                THP_FILE_FALLBACK,
                THP_FILE_FALLBACK_CHARGE,
                THP_FILE_MAPPED,
                THP_SPLIT_PAGE,
                THP_SPLIT_PAGE_FAILED,
                THP_DEFERRED_SPLIT_PAGE,
                THP_SPLIT_PMD,
                THP_SCAN_EXCEED_NONE_PTE,
                THP_SCAN_EXCEED_SWAP_PTE,
                THP_SCAN_EXCEED_SHARED_PTE,
#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
                THP_SPLIT_PUD,
#endif
                THP_ZERO_PAGE_ALLOC,
                THP_ZERO_PAGE_ALLOC_FAILED,
                THP_SWPOUT,
                THP_SWPOUT_FALLBACK,
#endif

And reading mm/shmem.c, obviously, shmem is using THP_FILE_ALLOC.

I will rename it to ANON_THP_ALLOC in v3, let me know if you disagree :-)

>
> --
> Cheers,
>
> David / dhildenb
>

Thanks
Barry