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uma: grow slabs to enforce minimum memory efficiency

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Memory efficiency can be poor with awkward item sizes (e.g. 1/2 or 1
page size + epsilon).  In order to achieve a minimum memory efficiency,
select a slab size with a potentially larger number of pages if it
yields a lower portion of waste.

This may mean using page_alloc instead of uma_small_alloc, which could
be more costly.

Discussed with:	jeff, mckusick
Sponsored by:	Dell EMC Isilon
Differential Revision:	https://reviews.freebsd.org/D23239
This commit is contained in:
Ryan Libby 2020-02-04 22:40:34 +00:00
parent 10c8fb47d9
commit 27ca37acb7
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=357549
1 changed files with 114 additions and 62 deletions
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176
sys/vm/uma_core.c
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@ -1830,6 +1830,39 @@ slab_ipers(size_t size, int align)
return (slab_ipers_hdr(size, rsize, UMA_SLAB_SIZE, true));
}
struct keg_layout_result {
u_int format;
u_int slabsize;
u_int ipers;
u_int eff;
};
static void
keg_layout_one(uma_keg_t keg, u_int rsize, u_int slabsize, u_int fmt,
struct keg_layout_result *kl)
{
u_int total;
kl->format = fmt;
kl->slabsize = slabsize;
/* Handle INTERNAL as inline with an extra page. */
if ((fmt & UMA_ZFLAG_INTERNAL) != 0) {
kl->format &= ~UMA_ZFLAG_INTERNAL;
kl->slabsize += PAGE_SIZE;
}
kl->ipers = slab_ipers_hdr(keg->uk_size, rsize, kl->slabsize,
(fmt & UMA_ZFLAG_OFFPAGE) == 0);
/* Account for memory used by an offpage slab header. */
total = kl->slabsize;
if ((fmt & UMA_ZFLAG_OFFPAGE) != 0)
total += slabzone(kl->ipers)->uz_keg->uk_rsize;
kl->eff = UMA_FRAC_FIXPT(kl->ipers * rsize, total);
}
/*
* Determine the format of a uma keg. This determines where the slab header
* will be placed (inline or offpage) and calculates ipers, rsize, and ppera.
@ -1843,15 +1876,14 @@ slab_ipers(size_t size, int align)
static void
keg_layout(uma_keg_t keg)
{
struct keg_layout_result kl = {}, kl_tmp;
u_int fmts[2];
u_int alignsize;
u_int eff;
u_int eff_offpage;
u_int format;
u_int ipers;
u_int ipers_offpage;
u_int nfmt;
u_int pages;
u_int rsize;
u_int slabsize;
u_int i, j;
KASSERT((keg->uk_flags & UMA_ZONE_PCPU) == 0 ||
(keg->uk_size <= UMA_PCPU_ALLOC_SIZE &&
@ -1866,8 +1898,6 @@ keg_layout(uma_keg_t keg)
PRINT_UMA_ZFLAGS));
alignsize = keg->uk_align + 1;
format = 0;
ipers = 0;
/*
* Calculate the size of each allocation (rsize) according to
@ -1877,10 +1907,7 @@ keg_layout(uma_keg_t keg)
rsize = MAX(keg->uk_size, UMA_SMALLEST_UNIT);
rsize = roundup2(rsize, alignsize);
if ((keg->uk_flags & UMA_ZONE_PCPU) != 0) {
slabsize = UMA_PCPU_ALLOC_SIZE;
pages = mp_maxid + 1;
} else if ((keg->uk_flags & UMA_ZONE_CACHESPREAD) != 0) {
if ((keg->uk_flags & UMA_ZONE_CACHESPREAD) != 0) {
/*
* We want one item to start on every align boundary in a page.
* To do this we will span pages. We will also extend the item
@ -1892,23 +1919,22 @@ keg_layout(uma_keg_t keg)
slabsize = rsize * (PAGE_SIZE / alignsize);
slabsize = MIN(slabsize, rsize * SLAB_MAX_SETSIZE);
slabsize = MIN(slabsize, UMA_CACHESPREAD_MAX_SIZE);
pages = howmany(slabsize, PAGE_SIZE);
slabsize = ptoa(pages);
slabsize = round_page(slabsize);
} else {
/*
* Choose a slab size of as many pages as it takes to represent
* a single item. We will then try to fit as many additional
* items into the slab as possible. At some point, we may want
* to increase the slab size for awkward item sizes in order to
* increase efficiency.
* Start with a slab size of as many pages as it takes to
* represent a single item. We will try to fit as many
* additional items into the slab as possible.
*/
pages = howmany(keg->uk_size, PAGE_SIZE);
slabsize = ptoa(pages);
slabsize = round_page(keg->uk_size);
}
/* Build a list of all of the available formats for this keg. */
nfmt = 0;
/* Evaluate an inline slab layout. */
if ((keg->uk_flags & (UMA_ZONE_NOTOUCH | UMA_ZONE_PCPU)) == 0)
ipers = slab_ipers_hdr(keg->uk_size, rsize, slabsize, true);
fmts[nfmt++] = 0;
/* TODO: vm_page-embedded slab. */
@ -1917,65 +1943,91 @@ keg_layout(uma_keg_t keg)
* asked to not go to the VM for buckets. If we do this we
* may end up going to the VM for slabs which we do not
* want to do if we're UMA_ZFLAG_CACHEONLY as a result
* of UMA_ZONE_VM, which clearly forbids it.
* of UMA_ZONE_VM, which clearly forbids it. In those cases,
* evaluate a pseudo-format called INTERNAL which has an inline
* slab header and one extra page to guarantee that it fits.
*
* Otherwise, see if using an OFFPAGE slab will improve our
* efficiency.
*/
if ((keg->uk_flags &
(UMA_ZFLAG_INTERNAL | UMA_ZFLAG_CACHEONLY)) != 0) {
if (ipers == 0) {
/* We need an extra page for the slab header. */
pages++;
slabsize = ptoa(pages);
ipers = slab_ipers_hdr(keg->uk_size, rsize, slabsize,
true);
}
goto out;
}
if ((keg->uk_flags & (UMA_ZFLAG_INTERNAL | UMA_ZFLAG_CACHEONLY)) != 0)
fmts[nfmt++] = UMA_ZFLAG_INTERNAL;
else
fmts[nfmt++] = UMA_ZFLAG_OFFPAGE;
/*
* See if using an OFFPAGE slab will improve our efficiency.
* Only do this if we are below our efficiency threshold.
* Choose a slab size and format which satisfy the minimum efficiency.
* Prefer the smallest slab size that meets the constraints.
*
* XXX We could try growing slabsize to limit max waste as well.
* Historically this was not done because the VM could not
* efficiently handle contiguous allocations.
* Start with a minimum slab size, to accommodate CACHESPREAD. Then,
* for small items (up to PAGE_SIZE), the iteration increment is one
* page; and for large items, the increment is one item.
*/
eff = UMA_FRAC_FIXPT(ipers * rsize, slabsize);
ipers_offpage = slab_ipers_hdr(keg->uk_size, rsize, slabsize, false);
eff_offpage = UMA_FRAC_FIXPT(ipers_offpage * rsize,
slabsize + slabzone(ipers_offpage)->uz_keg->uk_rsize);
if (ipers == 0 || (eff < UMA_MIN_EFF && eff < eff_offpage)) {
CTR5(KTR_UMA, "UMA decided we need offpage slab headers for "
"keg: %s(%p), minimum efficiency allowed = %u%%, "
"old efficiency = %u%%, offpage efficiency = %u%%",
keg->uk_name, keg, UMA_FIXPT_PCT(UMA_MIN_EFF),
UMA_FIXPT_PCT(eff), UMA_FIXPT_PCT(eff_offpage));
format = UMA_ZFLAG_OFFPAGE;
ipers = ipers_offpage;
i = (slabsize + rsize - keg->uk_size) / MAX(PAGE_SIZE, rsize);
KASSERT(i >= 1, ("keg %s(%p) flags=0x%b slabsize=%u, rsize=%u, i=%u",
keg->uk_name, keg, keg->uk_flags, PRINT_UMA_ZFLAGS, slabsize,
rsize, i));
for ( ; ; i++) {
slabsize = (rsize <= PAGE_SIZE) ? ptoa(i) :
round_page(rsize * (i - 1) + keg->uk_size);
for (j = 0; j < nfmt; j++) {
/* Only if we have no viable format yet. */
if ((fmts[j] & UMA_ZFLAG_INTERNAL) != 0 &&
kl.ipers > 0)
continue;
keg_layout_one(keg, rsize, slabsize, fmts[j], &kl_tmp);
if (kl_tmp.eff <= kl.eff)
continue;
kl = kl_tmp;
CTR6(KTR_UMA, "keg %s layout: format %#x "
"(ipers %u * rsize %u) / slabsize %#x = %u%% eff",
keg->uk_name, kl.format, kl.ipers, rsize,
kl.slabsize, UMA_FIXPT_PCT(kl.eff));
/* Stop when we reach the minimum efficiency. */
if (kl.eff >= UMA_MIN_EFF)
break;
}
if (kl.eff >= UMA_MIN_EFF ||
slabsize >= SLAB_MAX_SETSIZE * rsize ||
(keg->uk_flags & (UMA_ZONE_PCPU | UMA_ZONE_CONTIG)) != 0)
break;
}
out:
pages = atop(kl.slabsize);
if ((keg->uk_flags & UMA_ZONE_PCPU) != 0)
pages *= mp_maxid + 1;
keg->uk_rsize = rsize;
keg->uk_ipers = kl.ipers;
keg->uk_ppera = pages;
keg->uk_flags |= kl.format;
/*
* How do we find the slab header if it is offpage or if not all item
* start addresses are in the same page? We could solve the latter
* case with vaddr alignment, but we don't.
*/
if ((format & UMA_ZFLAG_OFFPAGE) != 0 ||
(ipers - 1) * rsize >= PAGE_SIZE) {
if ((keg->uk_flags & UMA_ZFLAG_OFFPAGE) != 0 ||
(keg->uk_ipers - 1) * rsize >= PAGE_SIZE) {
if ((keg->uk_flags & UMA_ZONE_NOTPAGE) != 0)
format |= UMA_ZFLAG_HASH;
keg->uk_flags |= UMA_ZFLAG_HASH;
else
format |= UMA_ZFLAG_VTOSLAB;
keg->uk_flags |= UMA_ZFLAG_VTOSLAB;
}
keg->uk_ipers = ipers;
keg->uk_rsize = rsize;
keg->uk_flags |= format;
keg->uk_ppera = pages;
CTR6(KTR_UMA, "%s: keg=%s, flags=%#x, rsize=%u, ipers=%u, ppera=%u",
__func__, keg->uk_name, keg->uk_flags, rsize, ipers, pages);
__func__, keg->uk_name, keg->uk_flags, rsize, keg->uk_ipers,
pages);
KASSERT(keg->uk_ipers > 0 && keg->uk_ipers <= SLAB_MAX_SETSIZE,
("%s: keg=%s, flags=0x%b, rsize=%u, ipers=%u, ppera=%u", __func__,
keg->uk_name, keg->uk_flags, PRINT_UMA_ZFLAGS, rsize, ipers,
pages));
keg->uk_name, keg->uk_flags, PRINT_UMA_ZFLAGS, rsize,
keg->uk_ipers, pages));
}
/*