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Subject[RFC] memblock; Properly handle overlaps
From
Date
Hi folks !

This is not fully tested yet (I'm toying with a little userspace
test bench, it seems to work well so far but I haven't yet tested
the cases with no-coalesce boundaries which at least ARM needs).

But it's good enough to get comments...

So currently, things like memblock_reserve() or memblock_free()
don't deal well -at-all- with overlaps of all kinds. Some specific
cases are handled but the code is clumsy and things will fall over
in many cases.

This is annoying because typically memblock_reserve() is used to
mark regions passed by the firmware as reserved and we all know
how much we can trust our firmwares right ?

I have also a case I need to deal with on powerpc where the flat
device-tree is fully enclosed within some other FW blob that has
its own reserve map entry, so when I end up trying to reserve
both, the current memblock code pukes.

In the end, I got tired, rewrote the low level functions to
add and remove a region in an array, and figured that my new
code looked simper and easier to understand than what was
there in the first place anyways :-) But feel free to object
or point out whether I've missed some obvious horrible case
etc...

Not-signed-off-yet-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---
diff --git a/mm/memblock.c b/mm/memblock.c
index 4618fda..481b64b 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -58,28 +58,6 @@ static unsigned long __init_memblock memblock_addrs_overlap(phys_addr_t base1, p
return ((base1 < (base2 + size2)) && (base2 < (base1 + size1)));
}

-static long __init_memblock memblock_addrs_adjacent(phys_addr_t base1, phys_addr_t size1,
- phys_addr_t base2, phys_addr_t size2)
-{
- if (base2 == base1 + size1)
- return 1;
- else if (base1 == base2 + size2)
- return -1;
-
- return 0;
-}
-
-static long __init_memblock memblock_regions_adjacent(struct memblock_type *type,
- unsigned long r1, unsigned long r2)
-{
- phys_addr_t base1 = type->regions[r1].base;
- phys_addr_t size1 = type->regions[r1].size;
- phys_addr_t base2 = type->regions[r2].base;
- phys_addr_t size2 = type->regions[r2].size;
-
- return memblock_addrs_adjacent(base1, size1, base2, size2);
-}
-
long __init_memblock memblock_overlaps_region(struct memblock_type *type, phys_addr_t base, phys_addr_t size)
{
unsigned long i;
@@ -206,14 +184,13 @@ static void __init_memblock memblock_remove_region(struct memblock_type *type, u
type->regions[i].size = type->regions[i + 1].size;
}
type->cnt--;
-}

-/* Assumption: base addr of region 1 < base addr of region 2 */
-static void __init_memblock memblock_coalesce_regions(struct memblock_type *type,
- unsigned long r1, unsigned long r2)
-{
- type->regions[r1].size += type->regions[r2].size;
- memblock_remove_region(type, r2);
+ /* Special case for empty arrays */
+ if (type->cnt == 0) {
+ type->cnt = 1;
+ type->regions[0].base = 0;
+ type->regions[0].size = 0;
+ }
}

/* Defined below but needed now */
@@ -296,58 +273,94 @@ extern int __init_memblock __weak memblock_memory_can_coalesce(phys_addr_t addr1
return 1;
}

-static long __init_memblock memblock_add_region(struct memblock_type *type, phys_addr_t base, phys_addr_t size)
+static long __init_memblock memblock_add_region(struct memblock_type *type,
+ phys_addr_t base, phys_addr_t size)
{
- unsigned long coalesced = 0;
- long adjacent, i;
+ phys_addr_t end = base + size;
+ long i;

+ /* If the array is empty, special case, replace the fake
+ * filler region and return
+ */
if ((type->cnt == 1) && (type->regions[0].size == 0)) {
type->regions[0].base = base;
type->regions[0].size = size;
return 0;
}

- /* First try and coalesce this MEMBLOCK with another. */
+ /* First try and coalesce this MEMBLOCK with others */
for (i = 0; i < type->cnt; i++) {
- phys_addr_t rgnbase = type->regions[i].base;
- phys_addr_t rgnsize = type->regions[i].size;
+ struct memblock_region *rgn = &type->regions[i];
+ phys_addr_t rend = rgn->base + rgn->size;
+
+ /* Exit if there's no possible hits */
+ if (rgn->base > end)
+ break;

- if ((rgnbase == base) && (rgnsize == size))
- /* Already have this region, so we're done */
+ /* Check if we are fully enclosed within an existing
+ * block
+ */
+ if (rgn->base <= base && rend >= end)
return 0;

- adjacent = memblock_addrs_adjacent(base, size, rgnbase, rgnsize);
- /* Check if arch allows coalescing */
- if (adjacent != 0 && type == &memblock.memory &&
- !memblock_memory_can_coalesce(base, size, rgnbase, rgnsize))
- break;
- if (adjacent > 0) {
- type->regions[i].base -= size;
- type->regions[i].size += size;
- coalesced++;
- break;
- } else if (adjacent < 0) {
- type->regions[i].size += size;
- coalesced++;
- break;
+ /* Check if we overlap or are adjacent with the bottom
+ * of a block.
+ */
+ if (base <= rgn->base && end >= rgn->base) {
+ /* Check if we are allowed to coalesce the two
+ * blocks. If not, we create a new block.
+ */
+ if (!memblock_memory_can_coalesce(base, size,
+ rgn->base,
+ rgn->size)) {
+ /* Overlap & can't coalesce are mutually
+ * exclusive, if you do that, be prepared
+ * for trouble
+ */
+ WARN_ON(end != rgn->base);
+ goto new_block;
+ }
+ /* We extend the bottom of the block down to our
+ * base
+ */
+ rgn->size += rgn->base - base;
+ rgn->base = base;
+
+ /* We continue processing from the end of the
+ * coalesced block.
+ */
+ base = rgn->base + rgn->size;
}
- }

- /* If we plugged a hole, we may want to also coalesce with the
- * next region
- */
- if ((i < type->cnt - 1) && memblock_regions_adjacent(type, i, i+1) &&
- ((type != &memblock.memory || memblock_memory_can_coalesce(type->regions[i].base,
- type->regions[i].size,
- type->regions[i+1].base,
- type->regions[i+1].size)))) {
- memblock_coalesce_regions(type, i, i+1);
- coalesced++;
- }
+ /* Check if e have nothing else to allocate (fully coalesced) */
+ if (base >= end)
+ return 0;

- if (coalesced)
- return coalesced;
+ /* Now check if we overlap or are adjacent with the
+ * top of a block
+ */
+ if (base <= rend && end >= rend) {
+ /* If we can't coalesce, create a new block */
+ if (!memblock_memory_can_coalesce(rgn->base,
+ rgn->size,
+ base, size)) {
+ /* Overlap & can't coalesce are mutually
+ * exclusive, if you do that, be prepared
+ * for trouble
+ */
+ WARN_ON(rend != base);
+ goto new_block;
+ }
+ /* We adjust our base down to enclose it
+ * and destroy the original block
+ */
+ size += (base - rgn->base);
+ base = rgn->base;
+ memblock_remove_region(type, i--);
+ }
+ }

+ new_block:
/* If we are out of space, we fail. It's too late to resize the array
* but then this shouldn't have happened in the first place.
*/
@@ -365,7 +378,6 @@ static long __init_memblock memblock_add_region(struct memblock_type *type, phys
break;
}
}
-
if (base < type->regions[0].base) {
type->regions[0].base = base;
type->regions[0].size = size;
@@ -389,52 +401,55 @@ long __init_memblock memblock_add(phys_addr_t base, phys_addr_t size)

}

-static long __init_memblock __memblock_remove(struct memblock_type *type, phys_addr_t base, phys_addr_t size)
+static long __init_memblock __memblock_remove(struct memblock_type *type,
+ phys_addr_t base, phys_addr_t size)
{
- phys_addr_t rgnbegin, rgnend;
phys_addr_t end = base + size;
int i;

- rgnbegin = rgnend = 0; /* supress gcc warnings */
-
- /* Find the region where (base, size) belongs to */
- for (i=0; i < type->cnt; i++) {
- rgnbegin = type->regions[i].base;
- rgnend = rgnbegin + type->regions[i].size;
+ /* Walk through the array for collisions */
+ for (i = 0; i < type->cnt; i++) {
+ struct memblock_region *rgn = &type->regions[i];
+ phys_addr_t rend = rgn->base + rgn->size;

- if ((rgnbegin <= base) && (end <= rgnend))
+ /* Nothing more to do, exit */
+ if (rgn->base > end)
break;
- }

- /* Didn't find the region */
- if (i == type->cnt)
- return -1;
+ /* If we fully enclose the block, drop it */
+ if (base <= rgn->base && end >= rend) {
+ memblock_remove_region(type, i--);
+ continue;
+ }

- /* Check to see if we are removing entire region */
- if ((rgnbegin == base) && (rgnend == end)) {
- memblock_remove_region(type, i);
- return 0;
- }
+ /* If we are fully enclosed within a block
+ * then we need to split it and we are done
+ */
+ if (base > rgn->base && end < rend) {
+ rgn->size = base - rgn->base;
+ if (!memblock_add_region(type, end, rend - end) )
+ return 0;
+ /* Failure to split is bad, we at least
+ * restore the block before erroring
+ */
+ rgn->size = rend - rgn->base;
+ WARN_ON(1);
+ return -1;
+ }

- /* Check to see if region is matching at the front */
- if (rgnbegin == base) {
- type->regions[i].base = end;
- type->regions[i].size -= size;
- return 0;
- }
+ /* Check if we need to trim the bottom of a block */
+ if (rgn->base < end && rend > end) {
+ rgn->size -= end - rgn->base;
+ rgn->base = end;
+ break;
+ }

- /* Check to see if the region is matching at the end */
- if (rgnend == end) {
- type->regions[i].size -= size;
- return 0;
- }
+ /* And check if we need to trim the top of a block */
+ if (base < rend)
+ rgn->size -= rend - base;

- /*
- * We need to split the entry - adjust the current one to the
- * beginging of the hole and add the region after hole.
- */
- type->regions[i].size = base - type->regions[i].base;
- return memblock_add_region(type, end, rgnend - end);
+ }
+ return 0;
}

long __init_memblock memblock_remove(phys_addr_t base, phys_addr_t size)
@@ -467,7 +482,7 @@ phys_addr_t __init __memblock_alloc_base(phys_addr_t size, phys_addr_t align, ph

found = memblock_find_base(size, align, 0, max_addr);
if (found != MEMBLOCK_ERROR &&
- memblock_add_region(&memblock.reserved, found, size) >= 0)
+ !memblock_add_region(&memblock.reserved, found, size))
return found;

return 0;
@@ -548,7 +563,7 @@ static phys_addr_t __init memblock_alloc_nid_region(struct memblock_region *mp,
if (this_nid == nid) {
phys_addr_t ret = memblock_find_region(start, this_end, size, align);
if (ret != MEMBLOCK_ERROR &&
- memblock_add_region(&memblock.reserved, ret, size) >= 0)
+ !memblock_add_region(&memblock.reserved, ret, size))
return ret;
}
start = this_end;



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