d/freebsd-skq
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Don't remove the virtual-to-physical mapping when an sf_buf is freed.

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Instead, allow the mapping to persist, but add the sf_buf to a free list.
If a later sendfile(2) or zero-copy send resends the same physical page,
perhaps with the same or different contents, then the mapping overhead is
avoided and the sf_buf is simply removed from the free list.

In other words, the i386 sf_buf implementation now behaves as a cache of
virtual-to-physical translations using an LRU replacement policy on
inactive sf_bufs.  This is similar in concept to a part of
http://www.cs.princeton.edu/~yruan/debox/ patch, but much simpler in
implementation.  Note: none of this is required on alpha, amd64, or ia64.
They now use their direct virtual-to-physical mapping to avoid any
emphemeral mapping overheads in their sf_buf implementations.
This commit is contained in:
alc 2003-12-07 22:49:25 +00:00
parent 93908284d5
commit d821fb3e55
2 changed files with 11 additions and 9 deletions
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19
sys/i386/i386/vm_machdep.c
View File

@ -110,7 +110,7 @@ static u_long sf_buf_hashmask;
#define SF_BUF_HASH(m) (((m) - vm_page_array) & sf_buf_hashmask)
static struct sf_head sf_buf_freelist;
static TAILQ_HEAD(, sf_buf) sf_buf_freelist;
static u_int sf_buf_alloc_want;
/*
@ -583,13 +583,13 @@ sf_buf_init(void *arg)
int i;
sf_buf_active = hashinit(nsfbufs, M_TEMP, &sf_buf_hashmask);
LIST_INIT(&sf_buf_freelist);
TAILQ_INIT(&sf_buf_freelist);
sf_base = kmem_alloc_nofault(kernel_map, nsfbufs * PAGE_SIZE);
sf_bufs = malloc(nsfbufs * sizeof(struct sf_buf), M_TEMP,
M_NOWAIT | M_ZERO);
for (i = 0; i < nsfbufs; i++) {
sf_bufs[i].kva = sf_base + i * PAGE_SIZE;
LIST_INSERT_HEAD(&sf_buf_freelist, &sf_bufs[i], list_entry);
TAILQ_INSERT_TAIL(&sf_buf_freelist, &sf_bufs[i], free_entry);
}
sf_buf_alloc_want = 0;
mtx_init(&sf_buf_lock, "sf_buf", NULL, MTX_DEF);
@ -609,11 +609,13 @@ sf_buf_alloc(struct vm_page *m)
mtx_lock(&sf_buf_lock);
LIST_FOREACH(sf, hash_list, list_entry) {
if (sf->m == m) {
if (sf->ref_count == 0)
TAILQ_REMOVE(&sf_buf_freelist, sf, free_entry);
sf->ref_count++;
goto done;
}
}
while ((sf = LIST_FIRST(&sf_buf_freelist)) == NULL) {
while ((sf = TAILQ_FIRST(&sf_buf_freelist)) == NULL) {
sf_buf_alloc_want++;
error = msleep(&sf_buf_freelist, &sf_buf_lock, PVM|PCATCH,
"sfbufa", 0);
@ -625,7 +627,9 @@ sf_buf_alloc(struct vm_page *m)
if (error)
goto done;
}
LIST_REMOVE(sf, list_entry);
TAILQ_REMOVE(&sf_buf_freelist, sf, free_entry);
if (sf->m != NULL)
LIST_REMOVE(sf, list_entry);
LIST_INSERT_HEAD(hash_list, sf, list_entry);
sf->ref_count = 1;
sf->m = m;
@ -649,10 +653,7 @@ sf_buf_free(void *addr, void *args)
m = sf->m;
sf->ref_count--;
if (sf->ref_count == 0) {
pmap_qremove((vm_offset_t)addr, 1);
sf->m = NULL;
LIST_REMOVE(sf, list_entry);
LIST_INSERT_HEAD(&sf_buf_freelist, sf, list_entry);
TAILQ_INSERT_TAIL(&sf_buf_freelist, sf, free_entry);
if (sf_buf_alloc_want > 0)
wakeup_one(&sf_buf_freelist);
}

1
sys/i386/include/sf_buf.h
View File

@ -35,6 +35,7 @@ struct vm_page;
struct sf_buf {
LIST_ENTRY(sf_buf) list_entry; /* list of buffers */
TAILQ_ENTRY(sf_buf) free_entry; /* list of buffers */
struct vm_page *m; /* currently mapped page */
vm_offset_t kva; /* va of mapping */
int ref_count; /* usage of this mapping */