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researchv10 Dan Cross

.TH LNODE 5 SHARE
.SH NAME
lnode \- kernel user shares structure
.SH SYNOPSIS
.B "#include <sys/lnode.h>"
.SH DESCRIPTION
The kernel
.I lnode
structure is used to maintain per-user shares while a user has processes running.
.I Lnodes
are installed by
.IR login (8)
via the 
.IR limits (2)
system call when a new user logs into the system.
.I Dead
lnodes are removed by 
.IR sharer (8)
when the last process for a user exits.
The layout as given in the include file is:
.PP
.nf
.ift .ta 1.1i 1.9i
.ifn .ta 24n 35n
/*
 * Structure for active shares
 */

typedef short	uid_t;

.ift .ta .3i 1.1i 1.9i
.ifn .ta 2n +10n +13n
struct lnode
{
	uid_t	l_uid;	/* real uid for owner of this node */
	u_short	l_flags;	/* (see below) */
	u_short	l_shares;	/* allocated shares */
	uid_t	l_group;	/* uid for this node's scheduling group */
	float	l_usage;	/* decaying accumulated costs */
	float	l_charge;	/* long term accumulated costs */
};

/*
 * Meaning of bits in l_flags
 */

.ift .ta .6i 1.8i 2.4i
.ifn .ta +8n +11n +6n
#define	\s-1ACTIVELNODE\s0	001	/* this lnode is on active list */
#define	\s-1LASTREF\s0	002	/* set for L_DEADLIM if last reference to this lnode */
#define	\s-1DEADGROUP\s0	004	/* group account is dead */
#define	\s-1CHNGDLIMITS\s0	020	/* this lnode's limits have changed */
#define	\s-1NOTSHARED\s0	040	/* this lnode does not get a share of the m/c */
.DT
.fi
.PP
.I Lnodes
are grouped together in a tree.
At any level in the tree,
the share of resources allocated to an individual lnode is that 
proportion of the group's resources
represented by the ratio of the lnode's shares
to the total shares of all the lnodes in the group.
The 
.I l_group
field represents the 
.I uid
of the group leader's lnode.
The top of the tree is represented by
.IR root 's
lnode, which is initialised at system boot time.
.PP
The
.SM LASTREF
bit in
.I l_flags
is set for the 
.SM L_DEADLIM
request to the
.IR limits (2)
system call if the last process referencing the 
.I lnode 
has exited.
The
.SM DEADGROUP
bit is set if this
.I lnode
was the last one referencing it's group.
Dead groups are collected via the
.SM L_DEADGROUP
request to the
.IR limits (2)
system call.
.PP
The
.I l_charge
field is the long term accumulated charge for consumption of resources.
For group leaders, it represents the charge for the whole group.
The 
.I l_usage
field is a number representing recent usage of resources,
and is used by the scheduler to determine current share of resources.
.SS kern_lnode
Each user's
.I lnode
is embedded in a larger structure to hold temporary values for use
by the scheduler, known as a
.IR kern_lnode .
The layout as given in the include file is:
.PP
.nf
.ift .ta 1.9i
.ifn .ta 28n
/*
 * Kernel user share structure
 */

typedef struct kern_lnode *	KL_p;

.ift .ta .3i 1.1i 1.9i
.ifn .ta 2n +13n +13n
struct kern_lnode
{
	KL_p	kl_next;	/* next in active list */
	KL_p	kl_prev;	/* prev in active list */
	KL_p	kl_parent;	/* group parent */
	KL_p	kl_gnext;	/* next in parent's group */
	KL_p	kl_ghead;	/* start of this group */
	struct lnode	kl;	/* user parameters (as above) */
	float	kl_gshares;	/* total shares for this group */
	float	kl_eshare;	/* effective share for this group */
	float	kl_norms;	/* share**2 for this lnode */
	float	kl_usage;	/* kl.l_usage / kl_norms */
	float	kl_rate;	/* active process rate for this lnode */
	float	kl_temp;	/* temporary for scheduler */
	float	kl_spare;	/* <spare> */
	u_long	kl_cost;	/* cost accumulating in current period */
	u_long	kl_muse;	/* memory pages used */
	u_short	kl_refcount;	/* processes attached to this lnode */
	u_short	kl_children;	/* lnodes attached to this lnode */
};
.DT
.fi
.PP
Every process has a pointer to its owner's
.I kern_lnode
called
.I p_lnode.
Every time a process incurs a clock tick,
the value
.I p_lnode\->kl_usage
multipied by
.I p_lnode\->kl_rate
is added to its scheduling priority in
.IR p_sharepri .
.I p_sharepri
is decayed by the clock by an amount depending on the process's
.I p_nice
value \(em the ``nicer'' the process, the slower the decay.
This value is copied into the low-level scheduler's priority in
.I p_pri
whenever the process is run in user space.
.SH "SEE ALSO"
limits(2),
share(5),
sharer(8).

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