Messages in this thread |  | | Date | Fri, 28 Jul 2017 12:27:43 +0200 | From | Michal Hocko <> | Subject | Re: [RFC PATCH] treewide: remove GFP_TEMPORARY allocation flag |
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On Fri 28-07-17 10:52:49, Mel Gorman wrote: > On Fri, Jul 28, 2017 at 11:19:04AM +0200, Michal Hocko wrote: > > From: Michal Hocko <mhocko@suse.com> > > > > GFP_TEMPORARY has been introduced by e12ba74d8ff3 ("Group short-lived > > and reclaimable kernel allocations") along with __GFP_RECLAIMABLE. It's > > primary motivation was to allow users to tell that an allocation is > > short lived and so the allocator can try to place such allocations close > > together and prevent long term fragmentation. As much as this sounds > > like a reasonable semantic it becomes much less clear when to use the > > highlevel GFP_TEMPORARY allocation flag. How long is temporary? Can > > the context holding that memory sleep? Can it take locks? It seems > > there is no good answer for those questions. > > > > The current implementation of GFP_TEMPORARY is basically > > GFP_KERNEL | __GFP_RECLAIMABLE which in itself is tricky because > > basically none of the existing caller provide a way to reclaim the > > allocated memory. So this is rather misleading and hard to evaluate for > > any benefits. > > > > At the time of the introduction, the users were all very short-lived > where short was for operations such as reading a proc file that discarded > buffers afterwards.
Maybe we can add a special slab cache for those?
> However, it does seem to have misused over the last > few years and it was too easy to confuse "temporary" with "short lived" > and too easy to get confused about "how short lived is short lived?". On > that basis; > > Acked-by: Mel Gorman <mgorman@suse.de>
Thanks! -- Michal Hocko SUSE Labs
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