Re: pre8: where has the anti-hog code gone?

[Ingo Molnar <mingo@elte.hu>]

On Sat, 13 May 2000, Linus Torvalds wrote:

> So pre-8 with your suggested for for kswapd() looks pretty good, actually,
> but still has this issue that try_to_free_pages() seems to give up too
> easily and return failure when it shouldn't. [...]

i believe the reason for gfp-NULL failures is the following:
do_try_to_free_pages() _does_ free pages, but we do the sync in the
writeback case _after_ releasing a particular page. This means other
processes can steal our freshly freed pages - rmqueue fails easily. So i'd
suggest the following workaround:

	if (try_to_free_pages() was succesful && final rmqueue() failed)
		goto repeat;

we could as well do the page_cache_release of the buffer-mapped cache
after sync_page_buffers(), but this only saves a single page - multipage
allocations will still have a big window to fail. The problem is that
freed RAM is anonymous right now. We can fundamentally solve this by
manipulating zone->free_pages the following way:

a __free_pages variant that does not increase zone->free_pages. this is
then later on done by the allocator (ie. __alloc_pages). This 'free page
transport' mechanizm guarantees that the non-atomic allocation path does
not 'lose' free pages along the way.

	Ingo

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