On Fri 23-09-16 22:14:40, zijun_hu wrote:

On 2016/9/23 21:33, Michal Hocko wrote:

quoted

On Fri 23-09-16 21:00:18, zijun_hu wrote:

quoted

On 09/23/2016 08:42 PM, Michal Hocko wrote:

quoted

quoted

quoted

quoted

no, it don't work for many special case
for example, provided  PMD_SIZE=2M
mapping [0x1f8800, 0x208800) virtual range will be split to two ranges
[0x1f8800, 0x200000) and [0x200000,0x208800) and map them separately
the first range will cause dead loop

I am not sure I see your point. How can we deadlock if _both_ addresses
get aligned to the page boundary and how does PMD_SIZE make any
difference.

i will take a example to illustrate my considerations
provided PUD_SIZE == 1G, PMD_SIZE == 2M, PAGE_SIZE == 4K
it is used by arm64 normally

we want to map virtual range [0xffffffff_ffc08800, 0xffffffff_fffff800) by
ioremap_page_range(),ioremap_pmd_range() is called to map the range
finally, ioremap_pmd_range() will call
ioremap_pte_range(pmd, 0xffffffff_ffc08800, 0xffffffff_fffe0000) and
ioremap_pte_range(pmd, 0xffffffff_fffe0000, 0xffffffff fffff800) separately

but those ranges are not aligned and it ioremap_page_range fix them up
to _be_ aligned then there is no problem, right? So either I am missing
something or we are talking past each other.

my complementary considerations are show below

why not to round up the range start boundary to page aligned?
1, it don't remain consistent with the original logic
   take map [0x1800, 0x4800) as example
   the original logic map range [0x1000, 0x2000), but rounding up start boundary
   don't mapping the range [0x1000, 0x2000)

just look at how we do that for the mmap...

okay
i don't familiar with mmap code very well now

mmap basically does addr &= PAGE_MASK (modulo mmap_min_addr) and
len = PAGE_ALIGN(len).

this is [star, end) raher than [start, start+len) but you should get the
point I guess.
-- 
Michal Hocko
SUSE Labs

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