On Thu, 2010-11-11 at 23:45 +0100, Ricardo M. Correia wrote: > On Thu, 2010-11-11 at 14:25 -0800, Andrew Morton wrote: > > And then we can set current->gfp_mask to GFP_ATOMIC when we take an > > interrupt, or take a spinlock. Also, doesn't this mean that spin_lock() would now have to save current->gfp_flags in the stack? So that we can restore the allocation mode when we do spin_unlock()? - Ricardo > > > > And leave it at GFP_KERNEL when in process context. > > > > And switch GFP_KERNEL to GFP_NOFS in the VM. > > > > And switch to GFP_NOIO in the block layer. > > > > So the allocation mode becomes implicit to the task state, so callers > > usually don't need to track it. > > > > So, ultimately, kmalloc(), alloc_pages() etc don't actually need a mode > > arg at all. We'll need new, special functions which _do_ take the > > gfp_t but they will be rarely-called specialised things. > > > > And probably we'll need interfaces like > > > > gfp_t mm_set_alloc_mode(gfp_t flags); > > void mm_restore_alloc_mode(gfp_t flags); > > > > gfp_t flags; > > > > flags = mm_set_alloc_mode(GFP_NOIO); > > ... > > mm_restore_alloc_mode(flags); > > Actually, I think it may not be that simple... > > Looking at some of the __GFP_* flags, it seems that some of them look > like allocation "options", i.e. something we may want or may not want to > do on a certain allocation, others look more like "capabilities", i.e. > something that we can or cannot do in a certain context. > > For example, __GFP_ZERO, __GFP_REPEAT, __GFP_HIGHMEM, ... is something > that we'd probably want a caller to specify on each allocation, because > only he knows what he actually wants to do. > > Others, like __GFP_FS, __GFP_IO, __GFP_WAIT, are things that we either > can or cannot do, depending on the context that we're in. > > The latter ones seem worth to start tracking on the task_struct, but the > former ones I think we'd still want to pass them to kmalloc() on each > invocation. > > Fortunately, if we put the latter ones in the task_struct, it removes > the need for having to propagate gfp_flags from function to function. > > And contrary to what you said previously (which at the time sounded > correct to me), this can actually save a lot of stack space, especially > on more register-starved architectures, because the only places where we > need to save the flags on the stack is when we enter/exit a certain > context, as opposed to having to always having to pass the gfp_mask down > the call stack like we do now. > > > argh, someone save us. > > :-) > > Thanks, > Ricardo > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>