On Tue, Sep 29, 2009 at 1:06 PM, askb <ask...@gmail.com> wrote: > > I need to do lot of small allocations (around 70-80 bytes) from a > > critical region > > while holding a spinlock. Total number of such allocation could go > > upto tens of > > thousands in few hours. So all these allocations use GFP_ATOMIC flag > > instead of > > GFP_KERNEL. As per my understanding, GFP_ATOMIC can never fail, and I > > dont > > want my allocations to fail. But this could be a bad idea right? Using > > GFP_ATOMIC > > for all these allocations? > > GFP_ATOMIC is ideal for situations while using a spinlock or in > interrupt context or in places like BH - softirqs and tasklets) as long > as you dont want to block or sleep. On the other hand GPF_KERNEL could > block. > > > > Is GFP_NOWAIT | GFP_KERNEL guarantee that? > > > > Is ( GFP_NOWAIT | GFP_KERNEL ) == ( GFP_ATOMIC - dont access emergency > > pools)? > Not sure if you can do something like this. > > > I think GFP_KERNEL | GFP_NOWAIT will solve my issue, what say? > > http://lxr.linux.no/#linux+v2.6.31/include/linux/gfp.h#L41 > > GFP_ATOMIC is __GFP_WAIT unset while using allocation from the resource > pool. So GFP_NOWAIT would be (GFP_ATOMIC & ~__GFP_HIGH) now not > allocating from the pool and wait not set. But GFP_KERNEL does include a > _GFP_WAIT which may not work. > > look into _GP_NOMEMALLOC - if you dont want to use memory pool. > > > You mean use only _GP_NOMEMALLOC as a sole flag to kmalloc?
As per your explaination, can't I use just <http://lxr.linux.no/linux+*/include/linux/gfp.h#L72>#define GFP_NOWAIT <http://lxr.linux.no/linux+*/+code=GFP_NOWAIT> (GFP_ATOMIC <http://lxr.linux.no/linux+*/+code=GFP_ATOMIC> & ~__GFP_HIGH <http://lxr.linux.no/linux+*/+code=__GFP_HIGH>) as a sole flag to kmalloc? Meaning I will not user GFP_KERNEL at all.. Would be that correct things to do? -Leo.
