git: 910535a82a29 - stable/13 - uma: Avoid excessive per-CPU draining

The branch stable/13 has been updated by des:

URL: https://cgit.FreeBSD.org/src/commit/?id=910535a82a29d71eb3951b2368aef358a207f18d

commit 910535a82a29d71eb3951b2368aef358a207f18d
Author:     Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2025-03-17 19:12:58 +0000
Commit:     Dag-Erling Smørgrav <des@FreeBSD.org>
CommitDate: 2025-03-31 18:36:01 +0000

    uma: Avoid excessive per-CPU draining
    
    After commit 389a3fa693ef, uma_reclaim_domain(UMA_RECLAIM_DRAIN_CPU)
    calls uma_zone_reclaim_domain(UMA_RECLAIM_DRAIN_CPU) twice on each zone
    in addition to globally draining per-CPU caches. This was unintended
    and is unnecessarily slow; in particular, draining per-CPU caches
    requires binding to each CPU.
    
    Stop draining per-CPU caches when visiting each zone, just do it once in
    pcpu_cache_drain_safe() to minimize the amount of expensive sched_bind()
    calls.
    
    Fixes:          389a3fa693ef ("uma: Add UMA_ZONE_UNMANAGED")
    MFC after:      1 week
    Sponsored by:   Klara, Inc.
    Sponsored by:   NetApp, Inc.
    Reviewed by:    gallatin, kib
    Differential Revision:  https://reviews.freebsd.org/D49349
    
    (cherry picked from commit f506d5af50fccc37f5aa9fe090e9a0d5f05506c8)
---
 sys/vm/uma_core.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/sys/vm/uma_core.c b/sys/vm/uma_core.c
index 2236df90dfc0..7334db2a9bbd 100644
--- a/sys/vm/uma_core.c
+++ b/sys/vm/uma_core.c
@@ -5198,6 +5198,13 @@ uma_reclaim_domain(int req, int domain)
 		zone_foreach(uma_reclaim_domain_cb, &args);
 		break;
 	case UMA_RECLAIM_DRAIN_CPU:
+		/*
+		 * Reclaim globally visible free items from all zones, then drain
+		 * per-CPU buckets, then reclaim items freed while draining.
+		 * This approach minimizes expensive context switching needed to
+		 * drain each zone's per-CPU buckets.
+		 */
+		args.req = UMA_RECLAIM_DRAIN;
 		zone_foreach(uma_reclaim_domain_cb, &args);
 		pcpu_cache_drain_safe(NULL);
 		zone_foreach(uma_reclaim_domain_cb, &args);