Remove slush space from clists.

Right now we only have a very small amount of drivers that use clists,
but we still allocate 50 cblocks as slush space, which allows drivers to
temporarily overcommit their storage. Most of the drivers don't allow
this anyway.

I've performed the following changes:

- We don't allocate any cblocks on startup.

- I've removed the DDB command, because it has nothing useful to print
  now. You can obtain the amount of allocated blocks by running `vmstat
  -m | grep clist'.

- I've removed cfreecount, which is now unused.

- The old code first tries to allocate using M_NOWAIT, followed by
  M_WAITOK. This doesn't make any sense, so just remove this logic. It
  seems the drivers allow us to sleep anyway.

We can even remove ccmax from clist_alloc_cblocks and c_cbmax from
struct clist, but this breaks binary compatibility.

This reduces the amount of allocated cblocks on my system from 54 to 4.

sys/kern/subr_clist.c

@@ -38,58 +38,15 @@ __FBSDID("$FreeBSD$");
 #include <sys/malloc.h>
 #include <sys/clist.h>
 
-static void clist_init(void *);
-SYSINIT(clist, SI_SUB_CLIST, SI_ORDER_FIRST, clist_init, NULL);
-
 static MALLOC_DEFINE(M_CLIST, "clist", "clist queue blocks");
 
 static struct cblock *cfreelist = NULL;
-int cfreecount = 0;
-static int cslushcount;
-static int ctotcount;
-
-#ifndef INITIAL_CBLOCKS
-#define	INITIAL_CBLOCKS 50
-#endif
 
 static struct cblock *cblock_alloc(void);
 static void cblock_alloc_cblocks(int number);
 static void cblock_free(struct cblock *cblockp);
 static void cblock_free_cblocks(int number);
 
-#include "opt_ddb.h"
-#ifdef DDB
-#include <ddb/ddb.h>
-
-DB_SHOW_COMMAND(cbstat, cbstat)
-{
-	int cbsize = CBSIZE;
-
-	printf(
-	"tot = %d (active = %d, free = %d (reserved = %d, slush = %d))\n",
-	       ctotcount * cbsize, ctotcount * cbsize - cfreecount, cfreecount,
-	       cfreecount - cslushcount * cbsize, cslushcount * cbsize);
-}
-#endif /* DDB */
-
-/*
- * Called from init_main.c
- */
-/* ARGSUSED*/
-static void
-clist_init(void *dummy)
-{
-	/*
-	 * Allocate an initial base set of cblocks as a 'slush'.
-	 * We allocate non-slush cblocks with each initial tty_open() and
-	 * deallocate them with each tty_close().
-	 * We should adjust the slush allocation.  This can't be done in
-	 * the i/o routines because they are sometimes called from
-	 * interrupt handlers when it may be unsafe to call malloc().
-	 */
-	cblock_alloc_cblocks(cslushcount = INITIAL_CBLOCKS);
-}
-
 /*
  * Remove a cblock from the cfreelist queue and return a pointer
  * to it.
@@ -104,7 +61,6 @@ cblock_alloc(void)
 		panic("clist reservation botch");
 	cfreelist = cblockp->c_next;
 	cblockp->c_next = NULL;
-	cfreecount -= CBSIZE;
 	return (cblockp);
 }
 
@@ -116,7 +72,6 @@ cblock_free(struct cblock *cblockp)
 {
 	cblockp->c_next = cfreelist;
 	cfreelist = cblockp;
-	cfreecount += CBSIZE;
 }
 
 /*
@@ -129,19 +84,13 @@ cblock_alloc_cblocks(int number)
 	struct cblock *cbp;
 
 	for (i = 0; i < number; ++i) {
-		cbp = malloc(sizeof *cbp, M_CLIST, M_NOWAIT);
-		if (cbp == NULL) {
-			printf(
-"cblock_alloc_cblocks: M_NOWAIT malloc failed, trying M_WAITOK\n");
-			cbp = malloc(sizeof *cbp, M_CLIST, M_WAITOK);
-		}
+		cbp = malloc(sizeof *cbp, M_CLIST, M_WAITOK);
 		/*
 		 * Freed cblocks have zero quotes and garbage elsewhere.
 		 * Set the may-have-quote bit to force zeroing the quotes.
 		 */
 		cblock_free(cbp);
 	}
-	ctotcount += number;
 }
 
 /*
@@ -184,7 +133,6 @@ cblock_free_cblocks(int number)
 
 	for (i = 0; i < number; ++i)
 		free(cblock_alloc(), M_CLIST);
-	ctotcount -= number;
 }
 
 /*
@@ -237,8 +185,7 @@ getc(struct clist *clistp)
 				clistp->c_cf = clistp->c_cl = NULL;
 			}
 			cblock_free(cblockp);
-			if (--clistp->c_cbcount >= clistp->c_cbreserved)
-				++cslushcount;
+			--clistp->c_cbcount;
 		}
 	}
 
@@ -285,8 +232,7 @@ q_to_b(struct clist *clistp, char *dest, int amount)
 				clistp->c_cf = clistp->c_cl = NULL;
 			}
 			cblock_free(cblockp);
-			if (--clistp->c_cbcount >= clistp->c_cbreserved)
-				++cslushcount;
+			--clistp->c_cbcount;
 		}
 	}
 
@@ -328,8 +274,7 @@ ndflush(struct clist *clistp, int amount)
 				clistp->c_cf = clistp->c_cl = NULL;
 			}
 			cblock_free(cblockp);
-			if (--clistp->c_cbcount >= clistp->c_cbreserved)
-				++cslushcount;
+			--clistp->c_cbcount;
 		}
 	}
 
@@ -364,12 +309,8 @@ putc(char chr, struct clist *clistp)
 			struct cblock *prev = (cblockp - 1);
 
 			if (clistp->c_cbcount >= clistp->c_cbreserved) {
-				if (clistp->c_cbcount >= clistp->c_cbmax
-				    || cslushcount <= 0) {
-					splx(s);
-					return (-1);
-				}
-				--cslushcount;
+				splx(s);
+				return (-1);
 			}
 			cblockp = cblock_alloc();
 			clistp->c_cbcount++;
@@ -430,12 +371,8 @@ b_to_q(char *src, int amount, struct clist *clistp)
 			struct cblock *prev = cblockp - 1;
 
 			if (clistp->c_cbcount >= clistp->c_cbreserved) {
-				if (clistp->c_cbcount >= clistp->c_cbmax
-				    || cslushcount <= 0) {
-					splx(s);
-					return (amount);
-				}
-				--cslushcount;
+				splx(s);
+				return (amount);
 			}
 			cblockp = cblock_alloc();
 			clistp->c_cbcount++;
@@ -510,8 +447,7 @@ unputc(struct clist *clistp)
 			 */
 			clistp->c_cl = (char *)(cbp+1);
 			cblock_free(cblockp);
-			if (--clistp->c_cbcount >= clistp->c_cbreserved)
-				++cslushcount;
+			--clistp->c_cbcount;
 			cbp->c_next = NULL;
 		}
 	}
@@ -523,8 +459,7 @@ unputc(struct clist *clistp)
 	if ((clistp->c_cc == 0) && clistp->c_cl) {
 		cblockp = (struct cblock *)((intptr_t)clistp->c_cl & ~CROUND);
 		cblock_free(cblockp);
-		if (--clistp->c_cbcount >= clistp->c_cbreserved)
-			++cslushcount;
+		--clistp->c_cbcount;
 		clistp->c_cf = clistp->c_cl = NULL;
 	}
 

sys/sys/clist.h

@@ -54,8 +54,6 @@ struct cblock {
 };
 
 #ifdef _KERNEL
-extern	int cfreecount;
-
 int	 b_to_q(char *cp, int cc, struct clist *q);
 void	 clist_alloc_cblocks(struct clist *q, int ccmax, int ccres);
 void	 clist_free_cblocks(struct clist *q);