Re: RFC: reviving mlock isolation dead code

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

Hello,

> I would like to resurect this, as I am seeing problems during a large
> mlock (many GB). The mlock takes a long time to complete
> (__mlock_vma_pages_range() is loading pages from disk), there is
> memory pressure as some pages have to be evicted to make room for the
> large mlock, and the LRU algorithm performs badly with the high amount
> of pages still on LRU list - PageMlocked has not been set yet - while
> their VMA is already VM_LOCKED.
> 
> One approach I am considering would be to modify
> __mlock_vma_pages_range() and it call sites so the mmap sem is only
> read-owned while __mlock_vma_pages_range() runs. The mlock handling
> code in try_to_unmap_one() would then be able to acquire the
> mmap_sem() and help, as it is designed to do.

I would like to talk historical story a bit. Originally, Lee designed it as you proposed. 
but Linus refused it. He thought ro-rwsem is bandaid fix. That is one of reason that
some developers seeks proper mmap_sem dividing way.



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