Re: GFP_XXX semantics (was: Re: [PATCH] 2.2.1{3,4,5} VM fix)

[Andi Kleen <ak@muc.de>]

On Mon, Jan 24, 2000 at 02:22:45PM +0100, Ingo Oeser wrote:
> On Sat, 22 Jan 2000, Andrea Arcangeli wrote:
> 
> [GFP-Mask semantics discussion]
> 
> ok, once we are about it here, could you please explain the
> _exact_ semantics for the GFP_XXX constants?
> 
> GFP_BUFFER
> GFP_ATOMIC
> GFP_BIGUSER
> GFP_USER
> GFP_KERNEL
> GFP_NFS
> GFP_KSWAPD
> 
> So which steps are tried to allocate these pages (freeing
> process, freeing globally, waiting, failing, kswapd-wakeup)? 
> 
> Because it is not easy to decide from a driver writers point of
> view, which one to use for which requests :(

As device driver writer you should only use two:
GFP_ATOMIC in interrupts/bottom halves/when you cannot sleep and
GFP_KERNEL when you're in user context and able to sleep.
All others are internal and only used by specific subsystems you
shouldn't care about.

-Andi

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