Re: [PATCH bpf-next 2/3] xdp: xdp_umem: replace kmap on vmap for umem map

[Ivan Khoronzhuk]

On Tue, Aug 13, 2019 at 10:42:18AM -0700, Jonathan Lemon wrote:
> On 13 Aug 2019, at 3:23, Ivan Khoronzhuk wrote:
>
> > For 64-bit there is no reason to use vmap/vunmap, so use page_address
> > as it was initially. For 32 bits, in some apps, like in samples
> > xdpsock_user.c when number of pgs in use is quite big, the kmap
> > memory can be not enough, despite on this, kmap looks like is
> > deprecated in such cases as it can block and should be used rather
> > for dynamic mm.
> >
> > Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@xxxxxxxxxx>
>
> Seems a bit overkill - if not high memory, kmap() falls back
> to just page_address(), unlike vmap().

> -- Jonathan

So, as kmap has limitation... if I correctly understood, you propose
to avoid macros and do smth like kmap:

	void *addr;
	if (!PageHighMem(&umem->pgs[i]))
		addr =  page_address(page);
	else
		addr = vmap(&umem->pgs[i], 1, VM_MAP, PAGE_KERNEL);

	umem->pages[i].addr = addr;

and while unmap

	if (!PageHighMem(&umem->pgs[i]))
		vunmap(umem->pages[i].addr);

I can try it, and add this in v2 if no objection.

> > ---
> > net/xdp/xdp_umem.c | 16 ++++++++++++----
> > 1 file changed, 12 insertions(+), 4 deletions(-)
> >
> > diff --git a/net/xdp/xdp_umem.c b/net/xdp/xdp_umem.c
> > index a0607969f8c0..907c9019fe21 100644
> > --- a/net/xdp/xdp_umem.c
> > +++ b/net/xdp/xdp_umem.c
> > @@ -14,7 +14,7 @@
> > #include <linux/netdevice.h>
> > #include <linux/rtnetlink.h>
> > #include <linux/idr.h>
> > -#include <linux/highmem.h>
> > +#include <linux/vmalloc.h>
> >
> > #include "xdp_umem.h"
> > #include "xsk_queue.h"
> > @@ -167,10 +167,12 @@ void xdp_umem_clear_dev(struct xdp_umem *umem)
> >
> > static void xdp_umem_unmap_pages(struct xdp_umem *umem)
> > {
> > +#if BITS_PER_LONG == 32
> > 	unsigned int i;
> >
> > 	for (i = 0; i < umem->npgs; i++)
> > -		kunmap(umem->pgs[i]);
> > +		vunmap(umem->pages[i].addr);
> > +#endif
> > }
> >
> > static void xdp_umem_unpin_pages(struct xdp_umem *umem)
> > @@ -378,8 +380,14 @@ static int xdp_umem_reg(struct xdp_umem *umem, 
> > struct xdp_umem_reg *mr)
> > 		goto out_account;
> > 	}
> >
> > -	for (i = 0; i < umem->npgs; i++)
> > -		umem->pages[i].addr = kmap(umem->pgs[i]);
> > +	for (i = 0; i < umem->npgs; i++) {
> > +#if BITS_PER_LONG == 32
> > +		umem->pages[i].addr = vmap(&umem->pgs[i], 1, VM_MAP,
> > +					   PAGE_KERNEL);
> > +#else
> > +		umem->pages[i].addr = page_address(umem->pgs[i]);
> > +#endif
> > +	}
> >
> > 	return 0;
> >
> > --
> > 2.17.1

--
Regards,
Ivan Khoronzhuk