Date: Mon, 22 Aug 2011 20:44:18 +0000 (UTC) From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r225089 - head/sys/vm Message-ID: <201108222044.p7MKiIXJ067739@svn.freebsd.org>
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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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