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Avoid use of contiguous memory allocations in busdma when possible.

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This patch improves the boundary checks in busdma to allow more cases
using the regular page based kernel memory allocator. Especially in
the case of having a non-zero boundary in the parent DMA tag. For
example AMD64 based platforms set the PCI DMA tag boundary to
PCI_DMA_BOUNDARY, 4GB, which before this patch caused contiguous
memory allocations to be preferred when allocating more than PAGE_SIZE
bytes. Even if the required alignment was less than PAGE_SIZE bytes.

This patch also fixes the nsegments check for using kmem_alloc_attr()
when the maximum segment size is less than PAGE_SIZE bytes.

Updated some comments describing the code in question.

Differential Revision:	https://reviews.freebsd.org/D10645
Reviewed by:		kib, jhb, gallatin, scottl
MFC after:		1 week
Sponsored by:		Mellanox Technologies
This commit is contained in:
Hans Petter Selasky 2017-05-16 14:21:37 +00:00
parent 7a36bd9ffd
commit 65b017b420
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=318353
5 changed files with 61 additions and 25 deletions
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6
sys/arm/arm/busdma_machdep-v4.c
View File

@ -736,8 +736,10 @@ bus_dmamem_alloc(bus_dma_tag_t dmat, void **vaddr, int flags,
if (bufzone != NULL && dmat->alignment <= bufzone->size &&
!_bus_dma_can_bounce(dmat->lowaddr, dmat->highaddr)) {
*vaddr = uma_zalloc(bufzone->umazone, mflags);
} else if (dmat->nsegments >= btoc(dmat->maxsize) &&
dmat->alignment <= PAGE_SIZE && dmat->boundary == 0) {
} else if (dmat->nsegments >=
howmany(dmat->maxsize, MIN(dmat->maxsegsz, PAGE_SIZE)) &&
dmat->alignment <= PAGE_SIZE &&
(dmat->boundary % PAGE_SIZE) == 0) {
*vaddr = (void *)kmem_alloc_attr(kernel_arena, dmat->maxsize,
mflags, 0, dmat->lowaddr, memattr);
} else {

10
sys/arm/arm/busdma_machdep-v6.c
View File

@ -779,7 +779,9 @@ bus_dmamem_alloc(bus_dma_tag_t dmat, void **vaddr, int flags,
* (the allocator aligns buffers to their size boundaries).
* - There's no need to handle lowaddr/highaddr exclusion zones.
* else allocate non-contiguous pages if...
* - The page count that could get allocated doesn't exceed nsegments.
* - The page count that could get allocated doesn't exceed
* nsegments also when the maximum segment size is less
* than PAGE_SIZE.
* - The alignment constraint isn't larger than a page boundary.
* - There are no boundary-crossing constraints.
* else allocate a block of contiguous pages because one or more of the
@ -788,8 +790,10 @@ bus_dmamem_alloc(bus_dma_tag_t dmat, void **vaddr, int flags,
if (bufzone != NULL && dmat->alignment <= bufzone->size &&
!exclusion_bounce(dmat)) {
*vaddr = uma_zalloc(bufzone->umazone, mflags);
} else if (dmat->nsegments >= btoc(dmat->maxsize) &&
dmat->alignment <= PAGE_SIZE && dmat->boundary == 0) {
} else if (dmat->nsegments >=
howmany(dmat->maxsize, MIN(dmat->maxsegsz, PAGE_SIZE)) &&
dmat->alignment <= PAGE_SIZE &&
(dmat->boundary % PAGE_SIZE) == 0) {
*vaddr = (void *)kmem_alloc_attr(kernel_arena, dmat->maxsize,
mflags, 0, dmat->lowaddr, memattr);
} else {

29
sys/arm64/arm64/busdma_bounce.c
View File

@ -461,22 +461,35 @@ bounce_bus_dmamem_alloc(bus_dma_tag_t dmat, void** vaddr, int flags,
(*mapp)->flags = DMAMAP_FROM_DMAMEM;
/*
* XXX:
* (dmat->alignment <= dmat->maxsize) is just a quick hack; the exact
* alignment guarantees of malloc need to be nailed down, and the
* code below should be rewritten to take that into account.
* Allocate the buffer from the malloc(9) allocator if...
* - It's small enough to fit into a single power of two sized bucket.
* - The alignment is less than or equal to the maximum size
* - The low address requirement is fulfilled.
* else allocate non-contiguous pages if...
* - The page count that could get allocated doesn't exceed
* nsegments also when the maximum segment size is less
* than PAGE_SIZE.
* - The alignment constraint isn't larger than a page boundary.
* - There are no boundary-crossing constraints.
* else allocate a block of contiguous pages because one or more of the
* constraints is something that only the contig allocator can fulfill.
*
* In the meantime, we'll warn the user if malloc gets it wrong.
* NOTE: The (dmat->common.alignment <= dmat->maxsize) check
* below is just a quick hack. The exact alignment guarantees
* of malloc(9) need to be nailed down, and the code below
* should be rewritten to take that into account.
*
* In the meantime warn the user if malloc gets it wrong.
*/
if ((dmat->common.maxsize <= PAGE_SIZE) &&
(dmat->common.alignment <= dmat->common.maxsize) &&
dmat->common.lowaddr >= ptoa((vm_paddr_t)Maxmem) &&
attr == VM_MEMATTR_DEFAULT) {
*vaddr = malloc(dmat->common.maxsize, M_DEVBUF, mflags);
} else if (dmat->common.nsegments >= btoc(dmat->common.maxsize) &&
} else if (dmat->common.nsegments >=
howmany(dmat->common.maxsize, MIN(dmat->common.maxsegsz, PAGE_SIZE)) &&
dmat->common.alignment <= PAGE_SIZE &&
(dmat->common.boundary == 0 ||
dmat->common.boundary >= dmat->common.lowaddr)) {
(dmat->common.boundary % PAGE_SIZE) == 0) {
/* Page-based multi-segment allocations allowed */
*vaddr = (void *)kmem_alloc_attr(kernel_arena,
dmat->common.maxsize, mflags, 0ul, dmat->common.lowaddr,

10
sys/mips/mips/busdma_machdep.c
View File

@ -690,7 +690,9 @@ bus_dmamem_alloc(bus_dma_tag_t dmat, void** vaddrp, int flags,
* (the allocator aligns buffers to their size boundaries).
* - There's no need to handle lowaddr/highaddr exclusion zones.
* else allocate non-contiguous pages if...
* - The page count that could get allocated doesn't exceed nsegments.
* - The page count that could get allocated doesn't exceed
* nsegments also when the maximum segment size is less
* than PAGE_SIZE.
* - The alignment constraint isn't larger than a page boundary.
* - There are no boundary-crossing constraints.
* else allocate a block of contiguous pages because one or more of the
@ -699,8 +701,10 @@ bus_dmamem_alloc(bus_dma_tag_t dmat, void** vaddrp, int flags,
if (bufzone != NULL && dmat->alignment <= bufzone->size &&
!_bus_dma_can_bounce(dmat->lowaddr, dmat->highaddr)) {
vaddr = uma_zalloc(bufzone->umazone, mflags);
} else if (dmat->nsegments >= btoc(dmat->maxsize) &&
dmat->alignment <= PAGE_SIZE && dmat->boundary == 0) {
} else if (dmat->nsegments >=
howmany(dmat->maxsize, MIN(dmat->maxsegsz, PAGE_SIZE)) &&
dmat->alignment <= PAGE_SIZE &&
(dmat->boundary % PAGE_SIZE) == 0) {
vaddr = (void *)kmem_alloc_attr(kernel_arena, dmat->maxsize,
mflags, 0, dmat->lowaddr, memattr);
} else {

31
sys/x86/x86/busdma_bounce.c
View File

@ -396,23 +396,36 @@ bounce_bus_dmamem_alloc(bus_dma_tag_t dmat, void** vaddr, int flags,
else
attr = VM_MEMATTR_DEFAULT;
/*
* XXX:
* (dmat->alignment <= dmat->maxsize) is just a quick hack; the exact
* alignment guarantees of malloc need to be nailed down, and the
* code below should be rewritten to take that into account.
/*
* Allocate the buffer from the malloc(9) allocator if...
* - It's small enough to fit into a single power of two sized bucket.
* - The alignment is less than or equal to the maximum size
* - The low address requirement is fulfilled.
* else allocate non-contiguous pages if...
* - The page count that could get allocated doesn't exceed
* nsegments also when the maximum segment size is less
* than PAGE_SIZE.
* - The alignment constraint isn't larger than a page boundary.
* - There are no boundary-crossing constraints.
* else allocate a block of contiguous pages because one or more of the
* constraints is something that only the contig allocator can fulfill.
*
* In the meantime, we'll warn the user if malloc gets it wrong.
* NOTE: The (dmat->common.alignment <= dmat->maxsize) check
* below is just a quick hack. The exact alignment guarantees
* of malloc(9) need to be nailed down, and the code below
* should be rewritten to take that into account.
*
* In the meantime warn the user if malloc gets it wrong.
*/
if ((dmat->common.maxsize <= PAGE_SIZE) &&
(dmat->common.alignment <= dmat->common.maxsize) &&
dmat->common.lowaddr >= ptoa((vm_paddr_t)Maxmem) &&
attr == VM_MEMATTR_DEFAULT) {
*vaddr = malloc(dmat->common.maxsize, M_DEVBUF, mflags);
} else if (dmat->common.nsegments >= btoc(dmat->common.maxsize) &&
} else if (dmat->common.nsegments >=
howmany(dmat->common.maxsize, MIN(dmat->common.maxsegsz, PAGE_SIZE)) &&
dmat->common.alignment <= PAGE_SIZE &&
(dmat->common.boundary == 0 ||
dmat->common.boundary >= dmat->common.lowaddr)) {
(dmat->common.boundary % PAGE_SIZE) == 0) {
/* Page-based multi-segment allocations allowed */
*vaddr = (void *)kmem_alloc_attr(kernel_arena,
dmat->common.maxsize, mflags, 0ul, dmat->common.lowaddr,