Jesper Dangaard Brouer 99c07c43c4 xdp: tracking page_pool resources and safe removal ... This patch is needed before we can allow drivers to use page_pool for DMA-mappings. Today with page_pool and XDP return API, it is possible to remove the page_pool object (from rhashtable), while there are still in-flight packet-pages. This is safely handled via RCU and failed lookups in __xdp_return() fallback to call put_page(), when page_pool object is gone. In-case page is still DMA mapped, this will result in page note getting correctly DMA unmapped. To solve this, the page_pool is extended with tracking in-flight pages. And XDP disconnect system queries page_pool and waits, via workqueue, for all in-flight pages to be returned. To avoid killing performance when tracking in-flight pages, the implement use two (unsigned) counters, that in placed on different cache-lines, and can be used to deduct in-flight packets. This is done by mapping the unsigned "sequence" counters onto signed Two's complement arithmetic operations. This is e.g. used by kernel's time_after macros, described in kernel commit 1ba3aab303 and 5a581b367b, and also explained in RFC1982. The trick is these two incrementing counters only need to be read and compared, when checking if it's safe to free the page_pool structure. Which will only happen when driver have disconnected RX/alloc side. Thus, on a non-fast-path. It is chosen that page_pool tracking is also enabled for the non-DMA use-case, as this can be used for statistics later. After this patch, using page_pool requires more strict resource "release", e.g. via page_pool_release_page() that was introduced in this patchset, and previous patches implement/fix this more strict requirement. Drivers no-longer call page_pool_destroy(). Drivers already call xdp_rxq_info_unreg() which call xdp_rxq_info_unreg_mem_model(), which will attempt to disconnect the mem id, and if attempt fails schedule the disconnect for later via delayed workqueue. Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com> Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org> Signed-off-by: David S. Miller <davem@davemloft.net>		2019-06-19 11:23:13 -04:00
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acpi
asm-generic
clocksource
crypto
drm
dt-bindings	Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net	2019-06-17 20:20:36 -07:00
keys
kvm
linux	flow_dissector: add support for ingress ifindex dissection	2019-06-19 10:09:21 -04:00
math-emu
media
memory
misc
net	xdp: tracking page_pool resources and safe removal	2019-06-19 11:23:13 -04:00
pcmcia
ras
rdma
scsi
soc
sound
target
trace	Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net	2019-06-17 20:20:36 -07:00
uapi	act_ctinfo: Don't use BIT() in UAPI headers.	2019-06-19 10:12:58 -04:00
video
xen