> Date: Mon, 14 Jun 2021 11:50:24 +0200
> From: Martin Pieuchot <m...@openbsd.org>
>
> Now that operations on amaps are serialized using a per-map rwlock
> the KERNEL_LOCK() shouldn't be necessary to call amap_unref(). The
> diff below allows the reaper to do this operation before grabbing it.
>
> I haven't seen any relevant contention on the reaper in my profilings,
> so I don't expect any visible change related to this change. However
> this reflects the current state of locking in UVM and helps me shrink
> my diff.
>
> ok?
This means we no longer call uvm_pause() for these, but I believe the
main reason for calling uvm_pause() is to prevent us from holding the
kernel lock for too long. So I think that's fine.
ok kettenis@
> Index: uvm/uvm_map.c
> ===================================================================
> RCS file: /cvs/src/sys/uvm/uvm_map.c,v
> retrieving revision 1.275
> diff -u -p -r1.275 uvm_map.c
> --- uvm/uvm_map.c 22 May 2021 08:38:29 -0000 1.275
> +++ uvm/uvm_map.c 14 Jun 2021 09:32:04 -0000
> @@ -1571,10 +1571,16 @@ uvm_unmap_detach(struct uvm_map_deadq *d
>
> TAILQ_FOREACH_SAFE(entry, deadq, dfree.deadq, tmp) {
> /* Skip entries for which we have to grab the kernel lock. */
> - if (entry->aref.ar_amap || UVM_ET_ISSUBMAP(entry) ||
> - UVM_ET_ISOBJ(entry))
> + if (UVM_ET_ISSUBMAP(entry) || UVM_ET_ISOBJ(entry))
> continue;
>
> + /* Drop reference to amap, if we've got one. */
> + if (entry->aref.ar_amap)
> + amap_unref(entry->aref.ar_amap,
> + entry->aref.ar_pageoff,
> + atop(entry->end - entry->start),
> + flags & AMAP_REFALL);
> +
> TAILQ_REMOVE(deadq, entry, dfree.deadq);
> uvm_mapent_free(entry);
> }
> @@ -1586,12 +1592,6 @@ uvm_unmap_detach(struct uvm_map_deadq *d
> while ((entry = TAILQ_FIRST(deadq)) != NULL) {
> if (waitok)
> uvm_pause();
> - /* Drop reference to amap, if we've got one. */
> - if (entry->aref.ar_amap)
> - amap_unref(entry->aref.ar_amap,
> - entry->aref.ar_pageoff,
> - atop(entry->end - entry->start),
> - flags & AMAP_REFALL);
>
> /* Drop reference to our backing object, if we've got one. */
> if (UVM_ET_ISSUBMAP(entry)) {
>
>
