Author: alc Date: Thu Sep 1 15:57:44 2016 New Revision: 305213 URL: https://svnweb.freebsd.org/changeset/base/305213
Log: As an optimization to the machine-independent layer, change the machine- dependent pmap_ts_referenced() so that it updates the page's dirty field if a modified bit is found while counting reference bits. This opportunistic update can be performed at low cost and can eliminate the need for some future calls to pmap_is_modified() by the machine- independent layer. Reviewed by: kib, markj MFC after: 3 weeks Sponsored by: EMC / Isilon Storage Division Differential Revision: https://reviews.freebsd.org/D7722 Modified: head/sys/amd64/amd64/pmap.c head/sys/i386/i386/pmap.c Modified: head/sys/amd64/amd64/pmap.c ============================================================================== --- head/sys/amd64/amd64/pmap.c Thu Sep 1 15:23:33 2016 (r305212) +++ head/sys/amd64/amd64/pmap.c Thu Sep 1 15:57:44 2016 (r305213) @@ -5843,6 +5843,14 @@ safe_to_clear_referenced(pmap_t pmap, pt * should be tested and standardized at some point in the future for * optimal aging of shared pages. * + * As an optimization, update the page's dirty field if a modified bit is + * found while counting reference bits. This opportunistic update can be + * performed at low cost and can eliminate the need for some future calls + * to pmap_is_modified(). However, since this function stops after + * finding PMAP_TS_REFERENCED_MAX reference bits, it may not detect some + * dirty pages. Those dirty pages will only be detected by a future call + * to pmap_is_modified(). + * * A DI block is not needed within this function, because * invalidations are performed before the PV list lock is * released. @@ -5855,7 +5863,7 @@ pmap_ts_referenced(vm_page_t m) pmap_t pmap; struct rwlock *lock; pd_entry_t oldpde, *pde; - pt_entry_t *pte, PG_A; + pt_entry_t *pte, PG_A, PG_M, PG_RW; vm_offset_t va; vm_paddr_t pa; int cleared, md_gen, not_cleared, pvh_gen; @@ -5890,9 +5898,19 @@ retry: } } PG_A = pmap_accessed_bit(pmap); + PG_M = pmap_modified_bit(pmap); + PG_RW = pmap_rw_bit(pmap); va = pv->pv_va; pde = pmap_pde(pmap, pv->pv_va); oldpde = *pde; + if ((oldpde & (PG_M | PG_RW)) == (PG_M | PG_RW)) { + /* + * Although "oldpde" is mapping a 2MB page, because + * this function is called at a 4KB page granularity, + * we only update the 4KB page under test. + */ + vm_page_dirty(m); + } if ((*pde & PG_A) != 0) { /* * Since this reference bit is shared by 512 4KB @@ -5986,11 +6004,15 @@ small_mappings: } } PG_A = pmap_accessed_bit(pmap); + PG_M = pmap_modified_bit(pmap); + PG_RW = pmap_rw_bit(pmap); pde = pmap_pde(pmap, pv->pv_va); KASSERT((*pde & PG_PS) == 0, ("pmap_ts_referenced: found a 2mpage in page %p's pv list", m)); pte = pmap_pde_to_pte(pde, pv->pv_va); + if ((*pte & (PG_M | PG_RW)) == (PG_M | PG_RW)) + vm_page_dirty(m); if ((*pte & PG_A) != 0) { if (safe_to_clear_referenced(pmap, *pte)) { atomic_clear_long(pte, PG_A); Modified: head/sys/i386/i386/pmap.c ============================================================================== --- head/sys/i386/i386/pmap.c Thu Sep 1 15:23:33 2016 (r305212) +++ head/sys/i386/i386/pmap.c Thu Sep 1 15:57:44 2016 (r305213) @@ -4798,6 +4798,14 @@ retry: * XXX: The exact number of bits to check and clear is a matter that * should be tested and standardized at some point in the future for * optimal aging of shared pages. + * + * As an optimization, update the page's dirty field if a modified bit is + * found while counting reference bits. This opportunistic update can be + * performed at low cost and can eliminate the need for some future calls + * to pmap_is_modified(). However, since this function stops after + * finding PMAP_TS_REFERENCED_MAX reference bits, it may not detect some + * dirty pages. Those dirty pages will only be detected by a future call + * to pmap_is_modified(). */ int pmap_ts_referenced(vm_page_t m) @@ -4824,6 +4832,14 @@ pmap_ts_referenced(vm_page_t m) pmap = PV_PMAP(pv); PMAP_LOCK(pmap); pde = pmap_pde(pmap, pv->pv_va); + if ((*pde & (PG_M | PG_RW)) == (PG_M | PG_RW)) { + /* + * Although "*pde" is mapping a 2/4MB page, because + * this function is called at a 4KB page granularity, + * we only update the 4KB page under test. + */ + vm_page_dirty(m); + } if ((*pde & PG_A) != 0) { /* * Since this reference bit is shared by either 1024 @@ -4872,6 +4888,8 @@ small_mappings: ("pmap_ts_referenced: found a 4mpage in page %p's pv list", m)); pte = pmap_pte_quick(pmap, pv->pv_va); + if ((*pte & (PG_M | PG_RW)) == (PG_M | PG_RW)) + vm_page_dirty(m); if ((*pte & PG_A) != 0) { atomic_clear_int((u_int *)pte, PG_A); pmap_invalidate_page(pmap, pv->pv_va); _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
