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SubjectRe: [RFC PATCH] treewide: remove GFP_TEMPORARY allocation flag

> > > "This allocation is temporary. It lasts milliseconds, not hours."
> >
> > It isn't sufficient to give a rule for when GFP_TEMPORARY will be used,
> > you also need to explain (at least in general terms) how the information
> > will be used. Also you need to give guidelines on whether the flag
> > should be set for allocation that will last seconds or minutes.
> >
> > If we have a flag that doesn't have a well defined meaning that actually
> > affects behavior, it will not be used consistently, and if we ever
> > change exactly how it behaves we can expect things to break. So it is
> > better not to have a flag, than to have a poorly defined flag.
> Absolutely agreed!
> > My current thoughts is that the important criteria is not how long the
> > allocation will be used for, but whether it is reclaimable. Allocations
> > that will only last 5 msecs are reclaimable by calling "usleep(5000)".
> > Other allocations might be reclaimable in other ways. Allocations that
> > are not reclaimable may well be directed to a more restricted pool of
> > memory, and might be more likely to fail. If we grew a strong
> > "reclaimable" concept, this 'temporary' concept that you want to hold on
> > to would become a burden.
> ... and here again. The whole motivation for the flag was to gather
> these objects together and reduce chances of internal fragmentation
> due to long lived objects mixed with short term ones. Without an
> explicit way to reclaim those objects or having a clear checkpoint to
> wait for it is not really helping us to reach desired outcome (less
> fragmented memory).


If you group allocations that last << 1 second, and ones that last >>
1 second, I'm pretty sure it reduces fragmentation... "reclaimable" or

Fragmentation is just statistical property, so getting it "mostly
right" helps...
(cesky, pictures)
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