On Thu, Nov 9, 2023 at 12:30 AM Paolo Abeni <pabeni@xxxxxxxxxx> wrote: > > I'm trying to wrap my head around the whole infra... the above line is > confusing. Why do you increment dma_addr? it will be re-initialized in > the next iteration. > That is just a mistake, sorry. Will remove this increment. On Thu, Nov 9, 2023 at 1:29 AM Yunsheng Lin <linyunsheng@xxxxxxxxxx> wrote:> >>> > >>> gen_pool_destroy BUG_ON() if it's not empty at the time of destroying. > >>> Technically that should never happen, because > >>> __netdev_devmem_binding_free() should only be called when the refcount > >>> hits 0, so all the chunks have been freed back to the gen_pool. But, > >>> just in case, I don't want to crash the server just because I'm > >>> leaking a chunk... this is a bit of defensive programming that is > >>> typically frowned upon, but the behavior of gen_pool is so severe I > >>> think the WARN() + check is warranted here. > >> > >> It seems it is pretty normal for the above to happen nowadays because of > >> retransmits timeouts, NAPI defer schemes mentioned below: > >> > >> https://lkml.kernel.org/netdev/168269854650.2191653.8465259808498269815.stgit@firesoul/ > >> > >> And currently page pool core handles that by using a workqueue. > > > > Forgive me but I'm not understanding the concern here. > > > > __netdev_devmem_binding_free() is called when binding->ref hits 0. > > > > binding->ref is incremented when an iov slice of the dma-buf is > > allocated, and decremented when an iov is freed. So, > > __netdev_devmem_binding_free() can't really be called unless all the > > iovs have been freed, and gen_pool_size() == gen_pool_avail(), > > regardless of what's happening on the page_pool side of things, right? > > I seems to misunderstand it. In that case, it seems to be about > defensive programming like other checking. > > By looking at it more closely, it seems napi_frag_unref() call > page_pool_page_put_many() directly， which means devmem seems to > be bypassing the napi_safe optimization. > > Can napi_frag_unref() reuse napi_pp_put_page() in order to reuse > the napi_safe optimization? > I think it already does. page_pool_page_put_many() is only called if !recycle or !napi_pp_put_page(). In that case page_pool_page_put_many() is just a replacement for put_page(), because this 'page' may be an iov. -- Thanks, Mina
