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For not offpage zones the slab is placed at the end of page. Keg's uk_pgoff

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is calculated to guarantee that struct uma_slab is placed at pointer size
alignment. Calculation of real struct uma_slab size is done in keg_ctor()
and yet again in keg_large_init(), to check if we need an extra page. This
calculation can actually be performed at compile time.

- Add SIZEOF_UMA_SLAB macro to calculate size of struct uma_slab placed at
  an end of a page with alignment requirement.
- Use SIZEOF_UMA_SLAB in keg_ctor() and in keg_large_init(). This is a not
  a functional change.
- Use SIZEOF_UMA_SLAB in UMA_SLAB_SPACE definition and in keg_small_init().
  This is a potential bugfix, but in reality I don't think there are any
  systems affected, since compiler aligns struct uma_slab anyway.
This commit is contained in:
Gleb Smirnoff 2018-11-28 19:17:27 +00:00
parent b92c2c907e
commit 3d5e3df73f
2 changed files with 29 additions and 40 deletions
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57
sys/vm/uma_core.c
View File

@ -1453,7 +1453,7 @@ keg_small_init(uma_keg_t keg)
if (keg->uk_flags & UMA_ZONE_OFFPAGE)
shsize = 0;
else
shsize = sizeof(struct uma_slab);
shsize = SIZEOF_UMA_SLAB;
if (rsize <= slabsize - shsize)
keg->uk_ipers = (slabsize - shsize) / rsize;
@ -1523,7 +1523,6 @@ keg_small_init(uma_keg_t keg)
static void
keg_large_init(uma_keg_t keg)
{
u_int shsize;
KASSERT(keg != NULL, ("Keg is null in keg_large_init"));
KASSERT((keg->uk_flags & UMA_ZFLAG_CACHEONLY) == 0,
@ -1536,23 +1535,17 @@ keg_large_init(uma_keg_t keg)
keg->uk_rsize = keg->uk_size;
/* Check whether we have enough space to not do OFFPAGE. */
if ((keg->uk_flags & UMA_ZONE_OFFPAGE) == 0) {
shsize = sizeof(struct uma_slab);
if (shsize & UMA_ALIGN_PTR)
shsize = (shsize & ~UMA_ALIGN_PTR) +
(UMA_ALIGN_PTR + 1);
if (PAGE_SIZE * keg->uk_ppera - keg->uk_rsize < shsize) {
/*
* We can't do OFFPAGE if we're internal, in which case
* we need an extra page per allocation to contain the
* slab header.
*/
if ((keg->uk_flags & UMA_ZFLAG_INTERNAL) == 0)
keg->uk_flags |= UMA_ZONE_OFFPAGE;
else
keg->uk_ppera++;
}
if ((keg->uk_flags & UMA_ZONE_OFFPAGE) == 0 &&
PAGE_SIZE * keg->uk_ppera - keg->uk_rsize < SIZEOF_UMA_SLAB) {
/*
* We can't do OFFPAGE if we're internal, in which case
* we need an extra page per allocation to contain the
* slab header.
*/
if ((keg->uk_flags & UMA_ZFLAG_INTERNAL) == 0)
keg->uk_flags |= UMA_ZONE_OFFPAGE;
else
keg->uk_ppera++;
}
if ((keg->uk_flags & UMA_ZONE_OFFPAGE) &&
@ -1693,20 +1686,11 @@ keg_ctor(void *mem, int size, void *udata, int flags)
/*
* If we're putting the slab header in the actual page we need to
* figure out where in each page it goes. This calculates a right
* justified offset into the memory on an ALIGN_PTR boundary.
* figure out where in each page it goes. See SIZEOF_UMA_SLAB
* macro definition.
*/
if (!(keg->uk_flags & UMA_ZONE_OFFPAGE)) {
u_int totsize;
/* Size of the slab struct and free list */
totsize = sizeof(struct uma_slab);
if (totsize & UMA_ALIGN_PTR)
totsize = (totsize & ~UMA_ALIGN_PTR) +
(UMA_ALIGN_PTR + 1);
keg->uk_pgoff = (PAGE_SIZE * keg->uk_ppera) - totsize;
keg->uk_pgoff = (PAGE_SIZE * keg->uk_ppera) - SIZEOF_UMA_SLAB;
/*
* The only way the following is possible is if with our
* UMA_ALIGN_PTR adjustments we are now bigger than
@ -1714,13 +1698,10 @@ keg_ctor(void *mem, int size, void *udata, int flags)
* mathematically possible for all cases, so we make
* sure here anyway.
*/
totsize = keg->uk_pgoff + sizeof(struct uma_slab);
if (totsize > PAGE_SIZE * keg->uk_ppera) {
printf("zone %s ipers %d rsize %d size %d\n",
zone->uz_name, keg->uk_ipers, keg->uk_rsize,
keg->uk_size);
panic("UMA slab won't fit.");
}
KASSERT(keg->uk_pgoff + sizeof(struct uma_slab) <=
PAGE_SIZE * keg->uk_ppera,
("zone %s ipers %d rsize %d size %d slab won't fit",
zone->uz_name, keg->uk_ipers, keg->uk_rsize, keg->uk_size));
}
if (keg->uk_flags & UMA_ZONE_HASH)

12
sys/vm/uma_int.h
View File

@ -139,9 +139,17 @@
#define UMA_MAX_WASTE 10
/*
* Size of memory in a not offpage slab available for actual items.
* Actual size of uma_slab when it is placed at an end of a page
* with pointer sized alignment requirement.
*/
#define UMA_SLAB_SPACE (UMA_SLAB_SIZE - sizeof(struct uma_slab))
#define SIZEOF_UMA_SLAB ((sizeof(struct uma_slab) & UMA_ALIGN_PTR) ? \
(sizeof(struct uma_slab) & ~UMA_ALIGN_PTR) + \
(UMA_ALIGN_PTR + 1) : sizeof(struct uma_slab))
/*
* Size of memory in a not offpage single page slab available for actual items.
*/
#define UMA_SLAB_SPACE (PAGE_SIZE - SIZEOF_UMA_SLAB)
/*
* I doubt there will be many cases where this is exceeded. This is the initial