From: Oscar Salvador <osalvador@suse.de>
To: David Hildenbrand <david@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Mike Rapoport <rppt@kernel.org>, Michal Hocko <mhocko@kernel.org>,
Wei Yang <richard.weiyang@linux.alibaba.com>
Subject: Re: [PATCH v1 2/2] mm/page_alloc: count CMA pages per zone and print them in /proc/zoneinfo
Date: Thu, 28 Jan 2021 14:44:58 +0100 [thread overview]
Message-ID: <20210128134458.GA8136@localhost.localdomain> (raw)
In-Reply-To: <2246d657-4f6d-c27d-4ae2-853a8437cda9@redhat.com>
On Thu, Jan 28, 2021 at 11:43:41AM +0100, David Hildenbrand wrote:
> > My knowledge of CMA tends to be quite low, actually I though that CMA
> > was somehow tied to ZONE_MOVABLE.
>
> CMA is often placed into one of the kernel zones, but can also end up in the movable zone.
Ok good to know.
> > I see how tracking CMA pages per zona might give you a clue, but what do
> > you mean by "might behave differently - even after some of these pages might
> > already have been allocated"
>
> Assume you have 4GB in ZONE_NORMAL but 1GB is assigned for CMA. You actually only have 3GB available for random kernel allocations, not 4GB.
>
> Currently, you can only observe the free CMA pages, excluding any pages that are already allocated. Having that information how many CMA pages we have can be helpful - similar to what we already have in /proc/meminfo.
I see, I agree that it can provide some guidance.
> > I see that NR_FREE_CMA_PAGES is there even without CONFIG_CMA, as you
> > said, but I am not sure about adding size to a zone unconditionally.
> > I mean, it is not terrible as IIRC, the maximum MAX_NUMNODES can get
> > is 1024, and on x86_64 that would be (1024 * 4 zones) * 8 = 32K.
> > So not a big deal, but still.
>
> I'm asking myself how many such systems will run without
> CONFIG_CMA in the future.
I am not sure, my comment was just to point out that even the added size might
not be that large, hiding it under CONFIG_CMA seemed the right thing to
do.
> > diff --git a/mm/vmstat.c b/mm/vmstat.c
> > index 8ba0870ecddd..5757df4bfd45 100644
> > --- a/mm/vmstat.c
> > +++ b/mm/vmstat.c
> > @@ -1559,13 +1559,15 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
> > "\n spanned %lu"
> > "\n present %lu"
> > "\n managed %lu",
> > + "\n cma %lu",
> > zone_page_state(zone, NR_FREE_PAGES),
> > min_wmark_pages(zone),
> > low_wmark_pages(zone),
> > high_wmark_pages(zone),
> > zone->spanned_pages,
> > zone->present_pages,
> > - zone->managed_pages);
> > + zone->managed_pages,
> > + IS_ENABLED(CONFIG_CMA) ? zone->cma_pages : 0);
> > seq_printf(m,
> > "\n protection: (%ld",
> >
> >
> > I do not see it that ugly, but just my taste.
>
> IIRC, that does not work. The compiler will still complain
> about a missing struct members. We would have to provide a
> zone_cma_pages() helper with some ifdefery.
Of course, it seems I switched off my brain.
> We could do something like this on top
>
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -530,7 +530,9 @@ struct zone {
> atomic_long_t managed_pages;
> unsigned long spanned_pages;
> unsigned long present_pages;
> +#ifdef CONFIG_CMA
> unsigned long cma_pages;
> +#endif
> const char *name;
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 97fc32a53320..b753a64f099f 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1643,7 +1643,10 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
> "\n spanned %lu"
> "\n present %lu"
> "\n managed %lu"
> - "\n cma %lu",
> +#ifdef CONFIG_CMA
> + "\n cma %lu"
> +#endif
> + "%s",
> zone_page_state(zone, NR_FREE_PAGES),
> min_wmark_pages(zone),
> low_wmark_pages(zone),
> @@ -1651,7 +1654,10 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
> zone->spanned_pages,
> zone->present_pages,
> zone_managed_pages(zone),
> - zone->cma_pages);
> +#ifdef CONFIG_CMA
> + zone->cma_pages,
> +#endif
> + "");
> seq_printf(m,
> "\n protection: (%ld",
Looks good to me, but I can see how those #ifdef can raise some
eyebrows.
Let us see what other thinks as well.
Btw, should linux-uapi be CCed, as /proc/vmstat layout will change?
--
Oscar Salvador
SUSE L3
next prev parent reply other threads:[~2021-01-28 13:45 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-27 10:18 [PATCH v1 0/2] mm/cma: better error handling and count pages per zone David Hildenbrand
2021-01-27 10:18 ` [PATCH v1 1/2] mm/cma: expose all pages to the buddy if activation of an area fails David Hildenbrand
2021-01-27 15:58 ` Zi Yan
2021-01-28 9:59 ` Oscar Salvador
2021-01-27 10:18 ` [PATCH v1 2/2] mm/page_alloc: count CMA pages per zone and print them in /proc/zoneinfo David Hildenbrand
2021-01-28 10:22 ` Oscar Salvador
2021-01-28 10:43 ` David Hildenbrand
2021-01-28 13:44 ` Oscar Salvador [this message]
2021-01-28 13:46 ` Oscar Salvador
2021-01-28 14:01 ` David Hildenbrand
2021-01-28 16:45 ` [PATCH v2] " David Hildenbrand
2021-01-28 21:42 ` Oscar Salvador
2021-01-28 21:54 ` David Rientjes
2021-01-28 22:03 ` David Hildenbrand
2021-01-28 22:28 ` David Rientjes
2021-01-28 22:30 ` David Hildenbrand
2021-01-29 11:34 ` [PATCH v3] " David Hildenbrand
2021-01-29 11:46 ` Oscar Salvador
2021-01-29 11:51 ` David Hildenbrand
2021-01-30 8:48 ` David Rientjes
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