Re: [PATCH RFC v3 06/35] mm: cma: Make CMA_ALLOC_SUCCESS/FAIL count the number of pages

Anshuman Khandual
2024-01-29T09:24:51Z

On 1/25/24 22:12, Alexandru Elisei wrote:
> The CMA_ALLOC_SUCCESS, respectively CMA_ALLOC_FAIL, are increased by one
> after each cma_alloc() function call. This is done even though cma_alloc()
> can allocate an arbitrary number of CMA pages. When looking at
> /proc/vmstat, the number of successful (or failed) cma_alloc() calls
> doesn't tell much with regards to how many CMA pages were allocated via
> cma_alloc() versus via the page allocator (regular allocation request or
> PCP lists refill).
>
> This can also be rather confusing to a user who isn't familiar with the
> code, since the unit of measurement for nr_free_cma is the number of pages,
> but cma_alloc_success and cma_alloc_fail count the number of cma_alloc()
> function calls.
>
> Let's make this consistent, and arguably more useful, by having
> CMA_ALLOC_SUCCESS count the number of successfully allocated CMA pages, and
> CMA_ALLOC_FAIL count the number of pages the cma_alloc() failed to
> allocate.
>
> For users that wish to track the number of cma_alloc() calls, there are
> tracepoints for that already implemented.
>
> Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
> ---
> mm/cma.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/cma.c b/mm/cma.c
> index f49c95f8ee37..dbf7fe8cb1bd 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -517,10 +517,10 @@ struct page *cma_alloc(struct cma *cma, unsigned long count,
> pr_debug("%s(): returned %p\n", __func__, page);
> out:
> if (page) {
> - count_vm_event(CMA_ALLOC_SUCCESS);
> + count_vm_events(CMA_ALLOC_SUCCESS, count);
> cma_sysfs_account_success_pages(cma, count);
> } else {
> - count_vm_event(CMA_ALLOC_FAIL);
> + count_vm_events(CMA_ALLOC_FAIL, count);
> if (cma)
> cma_sysfs_account_fail_pages(cma, count);
> }

Without getting into the merits of this patch - which is actually trying to do
semantics change to /proc/vmstat, wondering how is this even related to this
particular series ? If required this could be debated on it's on separately.