Re: [PATCH v2 2/2] mm/memory: reuse the whole exclusive large folio on a write fault

[David Hildenbrand (Arm)]

On 9/19/26 13:18, Yuan-Hao Hsu wrote:
> On Sat, 19 Sep 2026 12:10:56 +0200, David Hildenbrand (Arm) wrote:
>> Are you measuring the worst-case latency of a single write fault or only the
>> average over all writes?
> 
> The single fault.  Each store is timed by itself (clock_gettime()
> before and after), and the latency numbers come from a pattern where
> every store takes one of these faults (one store per folio), so there
> is nothing else in the average.  The tables show the median of those
> faults; I also have p99 and max (i7-12700KF, in a VM, us):
> 
>                      v7.3-rc3+              patched
>                      p50   p99   max        p50        p99        max
>   64K, 1 fault      0.42  0.57  25-26      0.71-0.74  0.96-1.10  28-60
>   2M, 1 fault       0.50  0.67  0.7-1.2    10.0-10.2  12.2-15.8  13-22
> 
> max is the slowest store of a run, median over 15 runs.  The 25 us on
> the base kernel are interrupts; the VM has those on both sides.  The
> 2M row is the worst case by construction, every one of those faults
> walks all 512 PTEs.

Thanks. See my other mail, we should focus on keeping the fault path as fast as
possible and minimizing the work in there.

-- 
Cheers,

David