Re: [PATCH v2] mm/vmpressure: skip socket pressure for costly order reclaim

[Johannes Weiner <hannes@cmpxchg.org>]

nOn Thu, Apr 02, 2026 at 04:25:11PM -0700, JP Kobryn (Meta) wrote:
> When kswapd reclaims at high order due to fragmentation, vmpressure() can
> report poor reclaim efficiency even though the system has plenty of free
> memory. This is because kswapd scans many pages but finds little to reclaim
> - the pages are actively in use and don't need to be freed. The resulting
> scan:reclaim ratio triggers socket pressure, throttling TCP throughput
> unnecessarily.
> 
> Net allocations do not exceed order 3 (PAGE_ALLOC_COSTLY_ORDER), so high
> order reclaim difficulty should not trigger socket 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.
> 
> Signed-off-by: JP Kobryn (Meta) <jp.kobryn@linux.dev>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>