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SubjectRe: [PATCH bpf-next 2/3] xdp: xdp_umem: replace kmap on vmap for umem map
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On 13 Aug 2019, at 11:30, Ivan Khoronzhuk wrote:

> 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@linaro.org>
>>
>> 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.

Seems like a reasonable compromise to me.
--
Jonathan


>
>>
>>> ---
>>> 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

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