Re: [Lhms-devel] [RFC] free_area[] bitmap elimination [0/3]

Hi,

Your approach seems much better than mine for hotplug-memory.

quoted

The use of page_count()==0 is a little worrisome.  There's almost
certainly some race conditions where a page can be mistaken for free
while it's page_count()==0, but before it's reached free_pages_bulk().

BTW, even if page_count()==0 isn't a valid check like you fear, you
could always steal a bit in the page->flags.  Check out 
free_pages_check() in mm/page_alloc.c for a nice summary of what state
pages have to be in before they're freed.  

Thanks for your comment.

In this patch, "whether a page is free and in buddy allocator ?" is confirmed by
page_count(page) == 0 and  page_order(page) == valid_order.
A valid_order is a value between (unsigned long)~0 - (unsigned long)~(MAX_ORDER)

But there may be pages which have vague page->private and conflict with my
buddy page checking.
I'd like to read free_pages_check() more and take page->flags into account.

This may have a good side effect.

If we can distinguish pages in the free_area lists from others precisely
and we can know order of the pages, we could capture pages without
traversing all pages in the free_area lists when removing a memory-section.
remove_page_freearea() Bradley Christiansen wrote would work more 
effectively.


Thank you,
Hirokazu Takahashi.
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"aart@kvack.org"> aart@kvack.org </a>