Re: WARNING: at mm/page-writeback.c:1990 __set_page_dirty_nobuffers+0x13a/0x170()

[KOSAKI Motohiro <kosaki.motohiro@gmail.com>]

> In changelog, Bartlomiej said.
>
>      My particular test case (on a ARM EXYNOS4 device with 512 MiB, which means
>      131072 standard 4KiB pages in 'Normal' zone) is to:
>
>      - allocate 120000 pages for kernel's usage
>      - free every second page (60000 pages) of memory just allocated
>      - allocate and use 60000 pages from user space
>      - free remaining 60000 pages of kernel memory
>        (now we have fragmented memory occupied mostly by user space pages)
>      - try to allocate 100 order-9 (2048 KiB) pages for kernel's usage
>
>      The results:
>      - with compaction disabled I get 11 successful allocations
>      - with compaction enabled - 14 successful allocations
>      - with this patch I'm able to get all 100 successful allocations
>
> I think above workload is really really artificial and theoretical so I didn't like
> this patch but Mel seem to like it. :(
>
> Quote from Mel
> " Ok, that is indeed an adverse workload that the current system will not
> properly deal with. I think you are right to try fixing this but may need
> a different approach that takes the cost out of the allocation/free path
> and moves it the compaction path."
>
> We can correct this patch to work but at least need justification about it.
> Do we really need this patch for such artificial workload?
> what do you think?

I'm ok to resubmit. But please change the thread.

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