From a1e9a3bba3fce73f004b59717130417b3faccb23 Mon Sep 17 00:00:00 2001 From: Konstantin Belousov Date: Wed, 14 Dec 2016 23:36:32 +0000 Subject: [PATCH] Provide introductory description of the default pager. Reviewed by: alc Sponsored by: The FreeBSD Foundation MFC after: 1 week --- sys/vm/default_pager.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/sys/vm/default_pager.c b/sys/vm/default_pager.c index d08e5f54a318..8887e95f1e9a 100644 --- a/sys/vm/default_pager.c +++ b/sys/vm/default_pager.c @@ -57,6 +57,16 @@ static boolean_t default_pager_haspage(vm_object_t, vm_pindex_t, int *, /* * pagerops for OBJT_DEFAULT - "default pager". + * + * This pager handles anonymous (no handle) swap-backed memory, just + * like the swap pager. It allows several optimizations based on the + * fact that no pages of a default object can be swapped out. The + * most important optimization is in vm_fault(), where the pager is + * never asked for a non-resident page. Instead, a freshly allocated + * zeroed page is used. + * + * On the first request to page out a page from a default object, the + * object is converted to swap pager type. */ struct pagerops defaultpagerops = { .pgo_alloc = default_pager_alloc,