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Summarize lifetime of cache entries.

This commit is contained in:
riastradh 2017-03-18 22:36:56 +00:00
parent 6eda01c527
commit 4829d818c5
1 changed files with 44 additions and 2 deletions
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46
sys/kern/vfs_cache.c
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@ -1,4 +1,4 @@
/* $NetBSD: vfs_cache.c,v 1.119 2017/03/18 22:04:52 riastradh Exp $ */
/* $NetBSD: vfs_cache.c,v 1.120 2017/03/18 22:36:56 riastradh Exp $ */
/*-
* Copyright (c) 2008 The NetBSD Foundation, Inc.
@ -58,7 +58,7 @@
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: vfs_cache.c,v 1.119 2017/03/18 22:04:52 riastradh Exp $");
__KERNEL_RCSID(0, "$NetBSD: vfs_cache.c,v 1.120 2017/03/18 22:36:56 riastradh Exp $");
#ifdef _KERNEL_OPT
#include "opt_ddb.h"
@ -102,6 +102,48 @@ __KERNEL_RCSID(0, "$NetBSD: vfs_cache.c,v 1.119 2017/03/18 22:04:52 riastradh Ex
* name is located in the cache, it will be dropped.
*/
/*
* Cache entry lifetime:
*
* nonexistent
* ---create---> active
* ---invalidate---> queued
* ---reclaim---> nonexistent.
*
* States:
* - Nonexistent. Cache entry does not exist.
*
* - Active. cache_lookup, cache_lookup_raw, cache_revlookup can look
* up, acquire references, and hand off references to vnodes,
* e.g. via v_interlock. Marked by nonnull ncp->nc_dvp.
*
* - Queued. Pending desstruction by cache_reclaim. Cannot be used by
* cache_lookup, cache_lookup_raw, or cache_revlookup. May still be
* on lists. Marked by null ncp->nc_dvp.
*
* Transitions:
*
* - Create: nonexistent--->active
*
* Done by cache_enter(dvp, vp, name, namelen, cnflags), called by
* VOP_LOOKUP after the answer is found. Allocates a struct
* namecache object, initializes it with the above fields, and
* activates it by inserting it into the forward and reverse tables.
*
* - Invalidate: active--->queued
*
* Done by cache_invalidate. If not already invalidated, nullify
* ncp->nc_dvp and ncp->nc_vp, and add to cache_gcqueue. Called,
* among various other places, in cache_lookup(dvp, name, namelen,
* nameiop, cnflags, &iswht, &vp) when MAKEENTRY is missing from
* cnflags.
*
* - Reclaim: queued--->nonexistent
*
* Done by cache_reclaim. Disassociate ncp from any lists it is on
* and free memory.
*/
/*
* Locking.
*