On Mon, 15 Mar 2021 18:30:03 -0700 Arjun Roy <arjunroy.kdev@xxxxxxxxx> wrote: > From: Arjun Roy <arjunroy@xxxxxxxxxx> > > TCP zerocopy receive is used by high performance network applications > to further scale. For RX zerocopy, the memory containing the network > data filled by the network driver is directly mapped into the address > space of high performance applications. To keep the TLB cost low, > these applications unmap the network memory in big batches. So, this > memory can remain mapped for long time. This can cause a memory > isolation issue as this memory becomes unaccounted after getting > mapped into the application address space. This patch adds the memcg > accounting for such memory. > > Accounting the network memory comes with its own unique challenges. > The high performance NIC drivers use page pooling to reuse the pages > to eliminate/reduce expensive setup steps like IOMMU. These drivers > keep an extra reference on the pages and thus we can not depend on the > page reference for the uncharging. The page in the pool may keep a > memcg pinned for arbitrary long time or may get used by other memcg. > > This patch decouples the uncharging of the page from the refcnt and > associates it with the map count i.e. the page gets uncharged when the > last address space unmaps it. Now the question is, what if the driver > drops its reference while the page is still mapped? That is fine as > the address space also holds a reference to the page i.e. the > reference count can not drop to zero before the map count. What tree were you hoping to get this merged through? I'd suggest net - it's more likely to get tested over there. > > ... > > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c These changes could be inside #ifdef CONFIG_NET. Although I expect MEMCG=y&&NET=n is pretty damn rare.
