Messages in this thread | | | From | Daniel Phillips <> | Subject | Re: [PATCH 00/10] foundations for reserve-based allocation | Date | Mon, 6 Aug 2007 11:40:04 -0700 |
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On Monday 06 August 2007 11:17, Peter Zijlstra wrote: > lim_{n -> inf} (2^(n+1)/((2^n)+1)) = 2^lim_{n -> inf} ((n+1)-n) = 2^1 = 2
Glad I asked :-)
> > Patch [3/10] adds a new field to struct page. > > No it doesn't.
True. It is not immediately obvious from the declaration that the overloaded field is always freed up before anybody else needs to use the union.
> > I do not think this is > > necessary. Allocating a page from reserve does not make it > > special. All we care about is that the total number of pages taken > > out of reserve is balanced by the total pages freed by a user of > > the reserve. > > And how do we know a page was taken out of the reserves? > > This is done by looking at page->reserve (overload of page->index) > and this value can be destroyed as soon as its observed. It is in a > sense an extra return value.
Ah I see. I used to let alloc_pages fail then repeat the allocation with __GFP_MEMALLOC set, which was easy but stupidly repetitious. Your technique is better, though returning the status in the page still looks a little funny. This is really about saving a page flag, no?
> > We do care about slab fragmentation in the sense that a slab page > > may be pinned in the slab by an unprivileged allocation and so that > > page may never be returned to the global page reserve. > > A slab page obtained from the reseserve will never serve an object to > an unprivilidged allocation. > > > One way to solve this is > > to have a per slabpage flag indicating the page came from reserve, > > and prevent mixing of privileged and unprivileged allocations on > > such a page. > > is done.
Serves me right for not reading that bit. So the score for that round is: peterz 3, phillips 0 ;-)
Regards,
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