Re: [PATCH v3] mm/vmpressure: skip socket pressure for costly order reclaim

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

On Mon,  6 Apr 2026 10:44:25 -0700 "JP Kobryn (Meta)" <jp.kobryn@linux.dev> wrote:

> When reclaim is triggered by high order allocations on a fragmented system,
> vmpressure() can report poor reclaim efficiency even though the system has
> plenty of free memory. This is because many pages are scanned, but few are
> found to actually reclaim - the pages are actively in use and don't need to
> be freed. The resulting scan:reclaim ratio causes vmpressure() to assert
> socket pressure, throttling TCP throughput unnecessarily.
> 
> Costly order allocations (above PAGE_ALLOC_COSTLY_ORDER) rely heavily on
> compaction to succeed, so poor reclaim efficiency at these orders does not
> necessarily indicate memory pressure. The kernel already treats this order
> as the boundary where reclaim is no longer expected to succeed and
> compaction may take over.
> 
> Make vmpressure() order-aware through an additional parameter sourced from
> scan_control at existing call sites. Socket pressure is now only asserted
> when order <= PAGE_ALLOC_COSTLY_ORDER.
> 
> Memcg reclaim is unaffected since try_to_free_mem_cgroup_pages() always
> uses order 0, which passes the filter unconditionally. Similarly,
> vmpressure_prio() now passes order 0 internally when calling vmpressure(),
> ensuring critical pressure from low reclaim priority is not suppressed by
> the order filter.

Thanks.  I'd prefer to park this until after next -rc1.  I could be
argued with, but....

What I'm not understanding from the above is how beneficial this patch
is.  Some description of observed before-and-after behavior, preferably
with impressive measurements?