Messages in this thread | | | Subject | Re: [RFC v2 PATCH] mm: shmem: make stat.st_blksize return huge page size if THP is on | From | Yang Shi <> | Date | Mon, 23 Apr 2018 10:19:27 -0600 |
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On 4/23/18 9:04 AM, Michal Hocko wrote: > On Sun 22-04-18 21:28:59, Yang Shi wrote: >> >> On 4/22/18 6:47 PM, Michal Hocko wrote: > [...] >>> will be used on the first aligned address even when the initial/last >>> portion of the mapping is not THP aligned. >> No, my test shows it is not. And, transhuge_vma_suitable() does check the >> virtual address alignment. If it is not huge page size aligned, it will not >> set PMD for huge page. > It's been quite some time since I've looked at that code but I think you > are wrong. It just doesn't make sense to make the THP decision on the > VMA alignment much. Kirill, can you clarify please?
In the test, QEMU is trying to mmap a file (16GB in my configuration) + a guard page. If the page size is 4KB, there not any pages are mapped by PMD, but if the page size is 2MB (huge page aligned) we can see a lot pages are mapped by PMD. The test result is showed in the commit log.
So, if your assumption is right, there must be something wrong in THP code.
> > Please note that I have no objections to actually export the huge page > size as the max block size but your changelog just doesn't make any > sense to me.
Thanks, Yang
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