Date: Sun, 16 Jun 2013 18:31:12 +0000 (UTC) From: Attilio Rao <attilio@FreeBSD.org> To: src-committers@freebsd.org, svn-src-user@freebsd.org Subject: svn commit: r251813 - user/attilio/vmobj-readlock/sys/vm Message-ID: <201306161831.r5GIVCZ3031047@svn.freebsd.org>
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Author: attilio Date: Sun Jun 16 18:31:12 2013 New Revision: 251813 URL: http://svnweb.freebsd.org/changeset/base/251813 Log: Tentatively document the hard/soft busy logic. Sponsored by: EMC / Isilon storage division Modified: user/attilio/vmobj-readlock/sys/vm/vm_page.h Modified: user/attilio/vmobj-readlock/sys/vm/vm_page.h ============================================================================== --- user/attilio/vmobj-readlock/sys/vm/vm_page.h Sun Jun 16 18:27:53 2013 (r251812) +++ user/attilio/vmobj-readlock/sys/vm/vm_page.h Sun Jun 16 18:31:12 2013 (r251813) @@ -109,6 +109,17 @@ * contains the dirty field. In the machine-independent layer, * the implementation of read-modify-write operations on the * field is encapsulated in vm_page_clear_dirty_mask(). + * + * Page content access is regulated (mostly) by the busy mechanism. + * When the page content is changing (for example, during a page READ + * operation) the page owner must acquire an hard busy token. Similarly, + * when the page content is just being accessed for reading purposes + * (for example, during a page WRITE operation) the page owner must + * acquire a soft busy token. + * The hard busy mechanism is controlled using vm_page_busy() and + * vm_page_unbusy() interfaces. Likewise the soft busy mechanism is + * controlled through the usage of vm_page_io_start() and + * vm_page_io_finish(). */ #if PAGE_SIZE == 4096
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