Re: [PATCH] memcg: Keep socket_pressure fresh on 32-bit kernel.

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 16 Jul 2025 04:29:12 +0000 Kuniyuki Iwashima <kuniyu@google.com> wrote:

> memcg->socket_pressure is initialised with jiffies when the memcg
> is created.
> 
> Once vmpressure detects that the cgroup is under memory pressure,
> the field is updated with jiffies + HZ to signal the fact to the
> socket layer and suppress memory allocation for one second.
> 
> Otherwise, the field is not updated.
> 
> mem_cgroup_under_socket_pressure() uses time_before() to check if
> jiffies is less than memcg->socket_pressure, and this has a bug on
> 32-bit kernel.
> 
>   if (time_before(jiffies, memcg->socket_pressure))
>           return true;
> 
> As time_before() casts the final result to long, the acceptable delta
> between two timestamps is 2 ^ (BITS_PER_LONG - 1).
> 
> On 32-bit kernel with CONFIG_HZ=1000, this is about 24 days.
> 
>   >>> (2 ** 31) / 1000 / 60 / 60 / 24
>   24.855134814814818
> 
> Once 24 days have passed since the last update of socket_pressure,
> mem_cgroup_under_socket_pressure() starts to lie until the next
> 24 days pass.
> 
> Thus, we need to update socket_pressure to a recent timestamp
> periodically on 32-bit kernel.
> 
> Let's do that every 24 hours, with a variation of about 0 to 4 hours.

Can't we simply convert ->socket_preesure to a 64-bit type? 
timespec64/time64_t/etc?