linux-kernel - Re: [PATCH v3] mm/page_alloc: count CMA pages per zone and print them in /proc/zoneinfo

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Date:   Sat, 30 Jan 2021 00:48:59 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     David Hildenbrand <david@...hat.com>
cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Mike Rapoport <rppt@...nel.org>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...nel.org>,
        Wei Yang <richard.weiyang@...ux.alibaba.com>,
        linux-api@...r.kernel.org
Subject: Re: [PATCH v3] mm/page_alloc: count CMA pages per zone and print
 them in /proc/zoneinfo

On Fri, 29 Jan 2021, David Hildenbrand wrote:

> Let's count the number of CMA pages per zone and print them in
> /proc/zoneinfo.
> 
> Having access to the total number of CMA pages per zone is helpful for
> debugging purposes to know where exactly the CMA pages ended up, and to
> figure out how many pages of a zone might behave differently, even after
> some of these pages might already have been allocated.
> 
> As one example, CMA pages part of a kernel zone cannot be used for
> ordinary kernel allocations but instead behave more like ZONE_MOVABLE.
> 
> For now, we are only able to get the global nr+free cma pages from
> /proc/meminfo and the free cma pages per zone from /proc/zoneinfo.
> 
> Example after this patch when booting a 6 GiB QEMU VM with
> "hugetlb_cma=2G":
>   # cat /proc/zoneinfo | grep cma
>           cma      0
>         nr_free_cma  0
>           cma      0
>         nr_free_cma  0
>           cma      524288
>         nr_free_cma  493016
>           cma      0
>           cma      0
>   # cat /proc/meminfo | grep Cma
>   CmaTotal:        2097152 kB
>   CmaFree:         1972064 kB
> 
> Note: We print even without CONFIG_CMA, just like "nr_free_cma"; this way,
>       one can be sure when spotting "cma 0", that there are definetly no
>       CMA pages located in a zone.
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>
> Cc: Mike Rapoport <rppt@...nel.org>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Wei Yang <richard.weiyang@...ux.alibaba.com>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: linux-api@...r.kernel.org
> Signed-off-by: David Hildenbrand <david@...hat.com>

Acked-by: David Rientjes <rientjes@...gle.com>