The branch stable/13 has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=2366d7ce87164b862e278a80ec896f5afcb5dbd5
commit 2366d7ce87164b862e278a80ec896f5afcb5dbd5 Author: Konstantin Belousov <[email protected]> AuthorDate: 2022-01-16 20:18:21 +0000 Commit: Konstantin Belousov <[email protected]> CommitDate: 2022-01-29 01:10:44 +0000 vm_pageout_scans: correct detection of active object (cherry picked from commit 3de96d664aaaf8e3fb1ca4fc4bd864d2cf734b24) --- sys/vm/vm_pageout.c | 56 ++++++++++++++++++++++++++++++++++++----------------- 1 file changed, 38 insertions(+), 18 deletions(-) diff --git a/sys/vm/vm_pageout.c b/sys/vm/vm_pageout.c index 899d35cd43b6..64a06dd7d55b 100644 --- a/sys/vm/vm_pageout.c +++ b/sys/vm/vm_pageout.c @@ -712,6 +712,38 @@ unlock_mp: return (error); } +/* + * Check if the object is active. Non-anonymous swap objects are + * always referenced by the owner, for them require ref_count > 1 in + * order to ignore the ownership ref. + * + * Perform an unsynchronized object ref count check. While + * the page lock ensures that the page is not reallocated to + * another object, in particular, one with unmanaged mappings + * that cannot support pmap_ts_referenced(), two races are, + * nonetheless, possible: + * 1) The count was transitioning to zero, but we saw a non- + * zero value. pmap_ts_referenced() will return zero + * because the page is not mapped. + * 2) The count was transitioning to one, but we saw zero. + * This race delays the detection of a new reference. At + * worst, we will deactivate and reactivate the page. + */ +static bool +vm_pageout_object_act(vm_object_t object) +{ + return (object->ref_count > + ((object->flags & (OBJ_SWAP | OBJ_ANON)) == OBJ_SWAP ? 1 : 0)); +} + +static int +vm_pageout_page_ts_referenced(vm_object_t object, vm_page_t m) +{ + if (!vm_pageout_object_act(object)) + return (0); + return (pmap_ts_referenced(m)); +} + /* * Attempt to launder the specified number of pages. * @@ -806,7 +838,7 @@ scan: if (vm_page_none_valid(m)) goto free_page; - refs = object->ref_count != 0 ? pmap_ts_referenced(m) : 0; + refs = vm_pageout_page_ts_referenced(object, m); for (old = vm_page_astate_load(m);;) { /* @@ -826,7 +858,7 @@ scan: } if (act_delta == 0) { ; - } else if (object->ref_count != 0) { + } else if (vm_pageout_object_act(object)) { /* * Increase the activation count if the page was * referenced while in the laundry queue. This @@ -1263,20 +1295,8 @@ act_scan: * Test PGA_REFERENCED after calling pmap_ts_referenced() so * that a reference from a concurrently destroyed mapping is * observed here and now. - * - * Perform an unsynchronized object ref count check. While - * the page lock ensures that the page is not reallocated to - * another object, in particular, one with unmanaged mappings - * that cannot support pmap_ts_referenced(), two races are, - * nonetheless, possible: - * 1) The count was transitioning to zero, but we saw a non- - * zero value. pmap_ts_referenced() will return zero - * because the page is not mapped. - * 2) The count was transitioning to one, but we saw zero. - * This race delays the detection of a new reference. At - * worst, we will deactivate and reactivate the page. */ - refs = object->ref_count != 0 ? pmap_ts_referenced(m) : 0; + refs = vm_pageout_page_ts_referenced(object, m); old = vm_page_astate_load(m); do { @@ -1526,7 +1546,7 @@ vm_pageout_scan_inactive(struct vm_domain *vmd, int page_shortage) if (vm_page_none_valid(m)) goto free_page; - refs = object->ref_count != 0 ? pmap_ts_referenced(m) : 0; + refs = vm_pageout_page_ts_referenced(object, m); for (old = vm_page_astate_load(m);;) { /* @@ -1546,7 +1566,7 @@ vm_pageout_scan_inactive(struct vm_domain *vmd, int page_shortage) } if (act_delta == 0) { ; - } else if (object->ref_count != 0) { + } else if (vm_pageout_object_act(object)) { /* * Increase the activation count if the * page was referenced while in the @@ -1584,7 +1604,7 @@ vm_pageout_scan_inactive(struct vm_domain *vmd, int page_shortage) * mappings allow write access, then the page may still be * modified until the last of those mappings are removed. */ - if (object->ref_count != 0) { + if (vm_pageout_object_act(object)) { vm_page_test_dirty(m); if (m->dirty == 0 && !vm_page_try_remove_all(m)) goto skip_page;
