Author: kib
Date: Mon Aug 22 20:44:18 2011
New Revision: 225089
URL: http://svn.freebsd.org/changeset/base/225089
Log:
Update some comments in swap_pager.c.
Reviewed and most wording by: alc
MFC after: 1 week
Approved by: re (bz)
Modified:
head/sys/vm/swap_pager.c
Modified: head/sys/vm/swap_pager.c
==============================================================================
--- head/sys/vm/swap_pager.c Mon Aug 22 20:33:05 2011 (r225088)
+++ head/sys/vm/swap_pager.c Mon Aug 22 20:44:18 2011 (r225089)
@@ -114,9 +114,9 @@ __FBSDID("$FreeBSD$");
#include <geom/geom.h>
/*
- * SWB_NPAGES must be a power of 2. It may be set to 1, 2, 4, 8, or 16
- * pages per allocation. We recommend you stick with the default of 8.
- * The 16-page limit is due to the radix code (kern/subr_blist.c).
+ * SWB_NPAGES must be a power of 2. It may be set to 1, 2, 4, 8, 16
+ * or 32 pages per allocation.
+ * The 32-page limit is due to the radix code (kern/subr_blist.c).
*/
#ifndef MAX_PAGEOUT_CLUSTER
#define MAX_PAGEOUT_CLUSTER 16
@@ -127,14 +127,11 @@ __FBSDID("$FreeBSD$");
#endif
/*
- * Piecemeal swap metadata structure. Swap is stored in a radix tree.
- *
- * If SWB_NPAGES is 8 and sizeof(char *) == sizeof(daddr_t), our radix
- * is basically 8. Assuming PAGE_SIZE == 4096, one tree level represents
- * 32K worth of data, two levels represent 256K, three levels represent
- * 2 MBytes. This is acceptable.
- *
- * Overall memory utilization is about the same as the old swap structure.
+ * The swblock structure maps an object and a small, fixed-size range
+ * of page indices to disk addresses within a swap area.
+ * The collection of these mappings is implemented as a hash table.
+ * Unused disk addresses within a swap area are allocated and managed
+ * using a blist.
*/
#define SWCORRECT(n) (sizeof(void *) * (n) / sizeof(daddr_t))
#define SWAP_META_PAGES (SWB_NPAGES * 2)
@@ -662,9 +659,7 @@ swap_pager_alloc(void *handle, vm_ooffse
* routine is typically called only when the entire object is
* about to be destroyed.
*
- * This routine may block, but no longer does.
- *
- * The object must be locked or unreferenceable.
+ * The object must be locked.
*/
static void
swap_pager_dealloc(vm_object_t object)
@@ -706,7 +701,7 @@ swap_pager_dealloc(vm_object_t object)
* Also has the side effect of advising that somebody made a mistake
* when they configured swap and didn't configure enough.
*
- * This routine may not block
+ * This routine may not sleep.
*
* We allocate in round-robin fashion from the configured devices.
*/
@@ -776,10 +771,7 @@ swp_pager_strategy(struct buf *bp)
*
* This routine returns the specified swap blocks back to the bitmap.
*
- * Note: This routine may not block (it could in the old swap code),
- * and through the use of the new blist routines it does not block.
- *
- * This routine may not block
+ * This routine may not sleep.
*/
static void
swp_pager_freeswapspace(daddr_t blk, int npages)
@@ -875,21 +867,16 @@ swap_pager_reserve(vm_object_t object, v
* cases where both the source and destination have a valid swapblk,
* we keep the destination's.
*
- * This routine is allowed to block. It may block allocating metadata
+ * This routine is allowed to sleep. It may sleep allocating metadata
* indirectly through swp_pager_meta_build() or if paging is still in
* progress on the source.
*
- * XXX vm_page_collapse() kinda expects us not to block because we
- * supposedly do not need to allocate memory, but for the moment we
- * *may* have to get a little memory from the zone allocator, but
- * it is taken from the interrupt memory. We should be ok.
- *
* The source object contains no vm_page_t's (which is just as well)
*
* The source object is of type OBJT_SWAP.
*
- * The source and destination objects must be locked or
- * inaccessible (XXX are they ?)
+ * The source and destination objects must be locked.
+ * Both object locks may temporarily be released.
*/
void
swap_pager_copy(vm_object_t srcobject, vm_object_t dstobject,
@@ -1066,7 +1053,7 @@ swap_pager_haspage(vm_object_t object, v
* does NOT change the m->dirty status of the page. Also: MADV_FREE
* depends on it.
*
- * This routine may not block
+ * This routine may not sleep.
*/
static void
swap_pager_unswapped(vm_page_t m)
@@ -1472,7 +1459,7 @@ swap_pager_putpages(vm_object_t object,
* operations, we vm_page_t->busy'd unbusy all pages ( we can do this
* because we marked them all VM_PAGER_PEND on return from putpages ).
*
- * This routine may not block.
+ * This routine may not sleep.
*/
static void
swp_pager_async_iodone(struct buf *bp)
@@ -1657,7 +1644,7 @@ swp_pager_async_iodone(struct buf *bp)
* Return 1 if at least one page in the given object is paged
* out to the given swap device.
*
- * This routine may not block.
+ * This routine may not sleep.
*/
int
swap_pager_isswapped(vm_object_t object, struct swdevt *sp)
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