On Tue, 17 Apr 2018, Christopher Lameter wrote: > On Tue, 17 Apr 2018, Vlastimil Babka wrote: > > > On 04/17/2018 04:45 PM, Christopher Lameter wrote: > > > > But then higher order allocs are generally seen as problematic. > > > > I think in this case they are better than wasting/fragmenting 384kB for > > 640kB object. > > Well typically we have suggested that people use vmalloc in the past. vmalloc is slow - it is unuseable for a buffer cache. > > > That > > > means that callers need to be able to tolerate failures. > > > > Is it any different from now? I suppose there would still be > > smallest-order fallback involved in sl*b itself? And if your allocation > > is so large it can fail even with the fallback (i.e. >= costly order), > > you need to tolerate failures anyway? > > Failures can occur even with < costly order as far as I can telkl. Order 0 > is the only safe one. The alloc_pages functions seems to retry indefinitely for order <= PAGE_ALLOC_COSTLY_ORDER. Do you have some explanation why it should fail? > > One corner case I see is if there is anyone who would rather use their > > own fallback instead of the space-wasting smallest-order fallback. > > Maybe we could map some GFP flag to indicate that. > > Well if you have a fallback then maybe the slab allocator should not fall > back on its own but let the caller deal with it. Mikulas
