Date: Sun, 15 Jul 2018 19:25:16 +0000 (UTC) From: Alan Cox <alc@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r336314 - head/sys/vm Message-ID: <201807151925.w6FJPGKq050256@repo.freebsd.org>
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Author: alc Date: Sun Jul 15 19:25:15 2018 New Revision: 336314 URL: https://svnweb.freebsd.org/changeset/base/336314 Log: Test PGA_REFERENCED after calling pmap_ts_referenced(), rather than before, so that a reference from a concurrently destroyed mapping is observed during the current scan. Reviewed by: kib, markj MFC after: 1 week Differential Revision: https://reviews.freebsd.org/D16277 Modified: head/sys/vm/vm_pageout.c Modified: head/sys/vm/vm_pageout.c ============================================================================== --- head/sys/vm/vm_pageout.c Sun Jul 15 19:04:23 2018 (r336313) +++ head/sys/vm/vm_pageout.c Sun Jul 15 19:25:15 2018 (r336314) @@ -793,18 +793,22 @@ recheck: * If the page has been referenced and the object is not dead, * reactivate or requeue the page depending on whether the * object is mapped. + * + * Test PGA_REFERENCED after calling pmap_ts_referenced() so + * that a reference from a concurrently destroyed mapping is + * observed here and now. */ - if ((m->aflags & PGA_REFERENCED) != 0) { - vm_page_aflag_clear(m, PGA_REFERENCED); - act_delta = 1; - } else - act_delta = 0; if (object->ref_count != 0) - act_delta += pmap_ts_referenced(m); + act_delta = pmap_ts_referenced(m); else { KASSERT(!pmap_page_is_mapped(m), ("page %p is mapped", m)); + act_delta = 0; } + if ((m->aflags & PGA_REFERENCED) != 0) { + vm_page_aflag_clear(m, PGA_REFERENCED); + act_delta++; + } if (act_delta != 0) { if (object->ref_count != 0) { VM_CNT_INC(v_reactivated); @@ -1215,14 +1219,11 @@ act_scan: /* * Check to see "how much" the page has been used. - */ - if ((m->aflags & PGA_REFERENCED) != 0) { - vm_page_aflag_clear(m, PGA_REFERENCED); - act_delta = 1; - } else - act_delta = 0; - - /* + * + * 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 @@ -1236,7 +1237,13 @@ act_scan: * worst, we will deactivate and reactivate the page. */ if (m->object->ref_count != 0) - act_delta += pmap_ts_referenced(m); + act_delta = pmap_ts_referenced(m); + else + act_delta = 0; + if ((m->aflags & PGA_REFERENCED) != 0) { + vm_page_aflag_clear(m, PGA_REFERENCED); + act_delta++; + } /* * Advance or decay the act_count based on recent usage. @@ -1482,17 +1489,21 @@ recheck: * If the page has been referenced and the object is not dead, * reactivate or requeue the page depending on whether the * object is mapped. + * + * Test PGA_REFERENCED after calling pmap_ts_referenced() so + * that a reference from a concurrently destroyed mapping is + * observed here and now. */ - if ((m->aflags & PGA_REFERENCED) != 0) { - vm_page_aflag_clear(m, PGA_REFERENCED); - act_delta = 1; - } else - act_delta = 0; - if (object->ref_count != 0) { - act_delta += pmap_ts_referenced(m); - } else { + if (object->ref_count != 0) + act_delta = pmap_ts_referenced(m); + else { KASSERT(!pmap_page_is_mapped(m), ("page %p is mapped", m)); + act_delta = 0; + } + if ((m->aflags & PGA_REFERENCED) != 0) { + vm_page_aflag_clear(m, PGA_REFERENCED); + act_delta++; } if (act_delta != 0) { if (object->ref_count != 0) {
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