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SubjectRe: [PATCH v3 2/5] memblock: Improve memblock to support allocation from lower address.
Hello tejun,

On 09/23/2013 11:50 PM, Tejun Heo wrote:
> Hello,
>
> Please separate out factoring out of top-down allocation. That change
> is an equivalent conversion which shouldn't involve any functional
> difference. Mixing that with introduction of new feature isn't a good
> idea, so the patch split should be 1. split out top-down allocation
> from memblock_find_in_range_node() 2. introduce bottom-up flag and
> implement the feature.

Ok, will do the split.

>
> On Fri, Sep 13, 2013 at 05:30:52PM +0800, Tang Chen wrote:
>> +/**
>> * memblock_find_in_range_node - find free area in given range and node
>> - * @start: start of candidate range
>> + * @start: start of candidate range, can be %MEMBLOCK_ALLOC_ACCESSIBLE
>
> The only reason @end has special ACCESSIBLE flag is because we don't
> know how high is actually accessible and it needs to be distinguished
> from ANYWHERE. We assume that the lower addresses are always mapped,
> so using ACCESSIBLE for @start is weird. I think it'd be clearer to
> make the memblock interface to set the direction explicitly state what
> it's doing - ie. something like set_memblock_alloc_above_kernel(bool
> enable). We clearly don't want pure bottom-up allocation and the
> @start/@end params in memblock interface are used to impose extra
> limitations for each allocation, not the overall allocator behavior.
>
>> @@ -100,8 +180,7 @@ phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t start,
>> phys_addr_t end, phys_addr_t size,
>> phys_addr_t align, int nid)
>> {
>> - phys_addr_t this_start, this_end, cand;
>> - u64 i;
>> + phys_addr_t ret;
>>
>> /* pump up @end */
>> if (end == MEMBLOCK_ALLOC_ACCESSIBLE)
>> @@ -111,18 +190,22 @@ phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t start,
>> start = max_t(phys_addr_t, start, PAGE_SIZE);
>> end = max(start, end);
>>
>> - for_each_free_mem_range_reverse(i, nid, &this_start, &this_end, NULL) {
>> - this_start = clamp(this_start, start, end);
>> - this_end = clamp(this_end, start, end);
>> + if (memblock_direction_bottom_up()) {
>> + /*
>> + * MEMBLOCK_ALLOC_ACCESSIBLE is 0, which is less than the end
>> + * of kernel image. So callers specify MEMBLOCK_ALLOC_ACCESSIBLE
>> + * as @start is OK.
>> + */
>> + start = max(start, __pa_symbol(_end)); /* End of kernel image. */
>>
>> - if (this_end < size)
>> - continue;
>> + ret = __memblock_find_range(start, end, size, align, nid);
>> + if (ret)
>> + return ret;
>>
>> - cand = round_down(this_end - size, align);
>> - if (cand >= this_start)
>> - return cand;
>> + pr_warn("memblock: Failed to allocate memory in bottom up direction. Now try top down direction.\n");
>
> You probably wanna explain why retrying top-down allocation may
> succeed when bottom-up failed.

ok. The reason is we always limit bottom-up allocation from
the kernel image end, but to-down allocation doesn't have the
limit, so retrying top-down allocation may succeed when
bottom-up failed.

Will add the comment to explain the retry.

Thanks.

>
> Thanks.
>


--
Thanks.
Zhang Yanfei


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