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Date:   Mon, 11 Mar 2019 22:49:24 -0700
From:   Y Song <ys114321@...il.com>
To:     Martynas Pumputis <m@...bda.lt>
Cc:     netdev <netdev@...r.kernel.org>, bpf@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, mhocko@...e.com
Subject: Re: [PATCH] bpf: Try harder when allocating memory for large maps

On Mon, Mar 11, 2019 at 12:32 PM Martynas Pumputis <m@...bda.lt> wrote:
>
> It has been observed that sometimes a higher order memory allocation
> for BPF maps fails when there is no obvious memory pressure in a system.
>
> E.g. the map (BPF_MAP_TYPE_LRU_HASH, key=38, value=56, max_elems=524288)
> could not be created due to vmalloc unable to allocate 75497472B,
> when the system's memory consumption (in MB) was the following:
>
>     Total: 3942 Used: 837 (21.24%) Free: 138 Buffers: 239 Cached: 2727
>
> Later analysis [1] by Michal Hocko showed that the vmalloc was not trying
> to reclaim memory from the page cache and was failing prematurely due to
> __GFP_NORETRY.
>
> Considering dcda9b0471 ("mm, tree wide: replace __GFP_REPEAT by
> __GFP_RETRY_MAYFAIL with more useful semantic") and [1], we can replace
> __GFP_NORETRY with __GFP_RETRY_MAYFAIL, as it won't invoke OOM killer
> and will try harder to fulfil allocation requests.
>
> The change has been tested with the workloads mentioned above and by
> observing oom_kill value from /proc/vmstat.
>
> [1]: https://lore.kernel.org/bpf/20190310071318.GW5232@dhcp22.suse.cz/
>
> Signed-off-by: Martynas Pumputis <m@...bda.lt>
Acked-by: Yonghong Song <yhs@...com>

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