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Message-ID: <CAHS8izMqHkPUma4WPr-Ao-foTzBY30vi-qH+BOFOrny5=Y0iKg@mail.gmail.com>
Date: Tue, 22 Aug 2023 16:33:27 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Jesper Dangaard Brouer <jbrouer@...hat.com>
Cc: brouer@...hat.com, netdev@...r.kernel.org, linux-media@...r.kernel.org,
dri-devel@...ts.freedesktop.org, "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
Jesper Dangaard Brouer <hawk@...nel.org>, Ilias Apalodimas <ilias.apalodimas@...aro.org>,
Arnd Bergmann <arnd@...db.de>, David Ahern <dsahern@...nel.org>,
Willem de Bruijn <willemdebruijn.kernel@...il.com>, Sumit Semwal <sumit.semwal@...aro.org>,
Christian König <christian.koenig@....com>,
Jason Gunthorpe <jgg@...pe.ca>, Hari Ramakrishnan <rharix@...gle.com>,
Dan Williams <dan.j.williams@...el.com>, Andy Lutomirski <luto@...nel.org>, stephen@...workplumber.org,
sdf@...gle.com
Subject: Re: [RFC PATCH v2 06/11] page-pool: add device memory support
On Tue, Aug 22, 2023 at 5:24 AM Jesper Dangaard Brouer
<jbrouer@...hat.com> wrote:
>
>
>
> On 22/08/2023 08.05, Mina Almasry wrote:
> > On Sat, Aug 19, 2023 at 2:51 AM Jesper Dangaard Brouer
> > <jbrouer@...hat.com> wrote:
> >>
> >> On 10/08/2023 03.57, Mina Almasry wrote:
> >>> Overload the LSB of struct page* to indicate that it's a page_pool_iov.
> >>>
> >>> Refactor mm calls on struct page * into helpers, and add page_pool_iov
> >>> handling on those helpers. Modify callers of these mm APIs with calls to
> >>> these helpers instead.
> >>>
> >>
> >> I don't like of this approach.
> >> This is adding code to the PP (page_pool) fast-path in multiple places.
> >>
> >> I've not had time to run my usual benchmarks, which are here:
> >>
> >> https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/lib/bench_page_pool_simple.c
> >>
> >
> > I ported over this benchmark to my tree and ran it, my results:
> >
>
> What CPU is this and GHz? (I guess 2.6 GHz based on results).
>
> (It looks like this CPU is more efficient, instructions per cycles, than
> my E5-1650 v4 @ 3.60GHz).
>
cat /proc/cpuinfo
...
vendor_id : GenuineIntel
cpu family : 6
model : 143
model name : Intel(R) Xeon(R) Platinum 8481C CPU @ 2.70GHz
stepping : 8
microcode : 0xffffffff
cpu MHz : 2699.998
```
This is a vCPU on the Google Cloud A3 VMs.
> > net-next @ b44693495af8
> > https://pastebin.com/raw/JuU7UQXe
> >
> > + Jakub's memory-provider APIs:
> > https://pastebin.com/raw/StMBhetn
> >
> > + devmem TCP changes:
> > https://pastebin.com/raw/mY1L6U4r
> >
>
> Only a single cycle slowdown for "page_pool01_fast_path".
> From 10 cycles to 11 cycles.
>
> > + intentional regression just to make sure the benchmark is working:
> > https://pastebin.com/raw/wqWhcJdG
> >
> > I don't seem to be able to detect a regression with this series as-is,
> > but I'm not that familiar with the test and may be doing something
> > wrong or misinterpreting the results. Does this look ok to you?
> >
>
> The performance results are better than I expected. The small
> regression from 10 cycles to 11 cycles is actually 10%, but I expect
> with some likely/unlikely instrumentation we can "likely" remove this again.
>
So the patch is already optimized carefully (I hope) to put all the
devmem processing in the default unlikely path. Willem showed me that:
if (page_pool_iov())
return handle_page_pool_iov();
return handle_page();
The handle_page() will be 'likely' by default, which removes the need
for explicit likely/unlikely. I'm not sure we can get better perf with
explicit likely/unlikey, but I can try.
> So, this change actually looks acceptable from a performance PoV.
> I still think this page_pool_iov is very invasive to page_pool, but
> maybe it is better to hide this "uglyness" inside page_pool.
>
> The test primarily tests fast-path, and you also add "if" statements to
> all the DMA operations, which is not part of this benchmark. Perhaps we
> can add unlikely statements, or inspect (objdump) the ASM to check code
> priorities the original page based "provider".
>
> >> But I'm sure it will affect performance.
> >>
>
> Guess, I was wrong ;-)
>
> --Jesper
>
>
> >> Regardless of performance, this approach is using ptr-LSB-bits, to hide
> >> that page-pointer are not really struct-pages, feels like force feeding
> >> a solution just to use the page_pool APIs.
> >>
> >>
> >>> In areas where struct page* is dereferenced, add a check for special
> >>> handling of page_pool_iov.
> >>>
> >>> The memory providers producing page_pool_iov can set the LSB on the
> >>> struct page* returned to the page pool.
> >>>
> >>> Note that instead of overloading the LSB of page pointers, we can
> >>> instead define a new union between struct page & struct page_pool_iov and
> >>> compact it in a new type. However, we'd need to implement the code churn
> >>> to modify the page_pool & drivers to use this new type. For this POC
> >>> that is not implemented (feedback welcome).
> >>>
> >>
> >> I've said before, that I prefer multiplexing on page->pp_magic.
> >> For your page_pool_iov the layout would have to match the offset of
> >> pp_magic, to do this. (And if insisting on using PP infra the refcnt
> >> would also need to align).
> >>
> >> On the allocation side, all drivers already use a driver helper
> >> page_pool_dev_alloc_pages() or we could add another (better named)
> >> helper to multiplex between other types of allocators, e.g. a devmem
> >> allocator.
> >>
> >> On free/return/recycle the functions napi_pp_put_page or skb_pp_recycle
> >> could multiplex on pp_magic and call another API. The API could be an
> >> extension to PP helpers, but it could also be a devmap allocator helper.
> >>
> >> IMHO forcing/piggy-bagging everything into page_pool is not the right
> >> solution. I really think netstack need to support different allocator
> >> types. The page pool have been leading the way, yes, but perhaps it is
> >> time to add an API layer that e.g. could be named netmem, that gives us
> >> the multiplexing between allocators. In that process some of page_pool
> >> APIs would be lifted out as common blocks and others remain.
> >>
> >> --Jesper
> >>
> >>> I have a sample implementation of adding a new page_pool_token type
> >>> in the page_pool to give a general idea here:
> >>> https://github.com/torvalds/linux/commit/3a7628700eb7fd02a117db036003bca50779608d
> >>>
> >>> Full branch here:
> >>> https://github.com/torvalds/linux/compare/master...mina:linux:tcpdevmem-pp-tokens
> >>>
> >>> (In the branches above, page_pool_iov is called devmem_slice).
> >>>
> >>> Could also add static_branch to speed up the checks in page_pool_iov
> >>> memory providers are being used.
> >>>
> >>> Signed-off-by: Mina Almasry <almasrymina@...gle.com>
> >>> ---
> >>> include/net/page_pool.h | 74 ++++++++++++++++++++++++++++++++++-
> >>> net/core/page_pool.c | 85 ++++++++++++++++++++++++++++-------------
> >>> 2 files changed, 131 insertions(+), 28 deletions(-)
> >>>
> >>> diff --git a/include/net/page_pool.h b/include/net/page_pool.h
> >>> index 537eb36115ed..f08ca230d68e 100644
> >>> --- a/include/net/page_pool.h
> >>> +++ b/include/net/page_pool.h
> >>> @@ -282,6 +282,64 @@ static inline struct page_pool_iov *page_to_page_pool_iov(struct page *page)
> >>> return NULL;
> >>> }
> >>>
> >>> +static inline int page_pool_page_ref_count(struct page *page)
> >>> +{
> >>> + if (page_is_page_pool_iov(page))
> >>> + return page_pool_iov_refcount(page_to_page_pool_iov(page));
> >>> +
> >>> + return page_ref_count(page);
> >>> +}
> >>> +
> >>> +static inline void page_pool_page_get_many(struct page *page,
> >>> + unsigned int count)
> >>> +{
> >>> + if (page_is_page_pool_iov(page))
> >>> + return page_pool_iov_get_many(page_to_page_pool_iov(page),
> >>> + count);
> >>> +
> >>> + return page_ref_add(page, count);
> >>> +}
> >>> +
> >>> +static inline void page_pool_page_put_many(struct page *page,
> >>> + unsigned int count)
> >>> +{
> >>> + if (page_is_page_pool_iov(page))
> >>> + return page_pool_iov_put_many(page_to_page_pool_iov(page),
> >>> + count);
> >>> +
> >>> + if (count > 1)
> >>> + page_ref_sub(page, count - 1);
> >>> +
> >>> + put_page(page);
> >>> +}
> >>> +
> >>> +static inline bool page_pool_page_is_pfmemalloc(struct page *page)
> >>> +{
> >>> + if (page_is_page_pool_iov(page))
> >>> + return false;
> >>> +
> >>> + return page_is_pfmemalloc(page);
> >>> +}
> >>> +
> >>> +static inline bool page_pool_page_is_pref_nid(struct page *page, int pref_nid)
> >>> +{
> >>> + /* Assume page_pool_iov are on the preferred node without actually
> >>> + * checking...
> >>> + *
> >>> + * This check is only used to check for recycling memory in the page
> >>> + * pool's fast paths. Currently the only implementation of page_pool_iov
> >>> + * is dmabuf device memory. It's a deliberate decision by the user to
> >>> + * bind a certain dmabuf to a certain netdev, and the netdev rx queue
> >>> + * would not be able to reallocate memory from another dmabuf that
> >>> + * exists on the preferred node, so, this check doesn't make much sense
> >>> + * in this case. Assume all page_pool_iovs can be recycled for now.
> >>> + */
> >>> + if (page_is_page_pool_iov(page))
> >>> + return true;
> >>> +
> >>> + return page_to_nid(page) == pref_nid;
> >>> +}
> >>> +
> >>> struct page_pool {
> >>> struct page_pool_params p;
> >>>
> >>> @@ -434,6 +492,9 @@ static inline long page_pool_defrag_page(struct page *page, long nr)
> >>> {
> >>> long ret;
> >>>
> >>> + if (page_is_page_pool_iov(page))
> >>> + return -EINVAL;
> >>> +
> >>> /* If nr == pp_frag_count then we have cleared all remaining
> >>> * references to the page. No need to actually overwrite it, instead
> >>> * we can leave this to be overwritten by the calling function.
> >>> @@ -494,7 +555,12 @@ static inline void page_pool_recycle_direct(struct page_pool *pool,
> >>>
> >>> static inline dma_addr_t page_pool_get_dma_addr(struct page *page)
> >>> {
> >>> - dma_addr_t ret = page->dma_addr;
> >>> + dma_addr_t ret;
> >>> +
> >>> + if (page_is_page_pool_iov(page))
> >>> + return page_pool_iov_dma_addr(page_to_page_pool_iov(page));
> >>> +
> >>> + ret = page->dma_addr;
> >>>
> >>> if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT)
> >>> ret |= (dma_addr_t)page->dma_addr_upper << 16 << 16;
> >>> @@ -504,6 +570,12 @@ static inline dma_addr_t page_pool_get_dma_addr(struct page *page)
> >>>
> >>> static inline void page_pool_set_dma_addr(struct page *page, dma_addr_t addr)
> >>> {
> >>> + /* page_pool_iovs are mapped and their dma-addr can't be modified. */
> >>> + if (page_is_page_pool_iov(page)) {
> >>> + DEBUG_NET_WARN_ON_ONCE(true);
> >>> + return;
> >>> + }
> >>> +
> >>> page->dma_addr = addr;
> >>> if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT)
> >>> page->dma_addr_upper = upper_32_bits(addr);
> >>> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> >>> index 0a7c08d748b8..20c1f74fd844 100644
> >>> --- a/net/core/page_pool.c
> >>> +++ b/net/core/page_pool.c
> >>> @@ -318,7 +318,7 @@ static struct page *page_pool_refill_alloc_cache(struct page_pool *pool)
> >>> if (unlikely(!page))
> >>> break;
> >>>
> >>> - if (likely(page_to_nid(page) == pref_nid)) {
> >>> + if (likely(page_pool_page_is_pref_nid(page, pref_nid))) {
> >>> pool->alloc.cache[pool->alloc.count++] = page;
> >>> } else {
> >>> /* NUMA mismatch;
> >>> @@ -363,7 +363,15 @@ static void page_pool_dma_sync_for_device(struct page_pool *pool,
> >>> struct page *page,
> >>> unsigned int dma_sync_size)
> >>> {
> >>> - dma_addr_t dma_addr = page_pool_get_dma_addr(page);
> >>> + dma_addr_t dma_addr;
> >>> +
> >>> + /* page_pool_iov memory provider do not support PP_FLAG_DMA_SYNC_DEV */
> >>> + if (page_is_page_pool_iov(page)) {
> >>> + DEBUG_NET_WARN_ON_ONCE(true);
> >>> + return;
> >>> + }
> >>> +
> >>> + dma_addr = page_pool_get_dma_addr(page);
> >>>
> >>> dma_sync_size = min(dma_sync_size, pool->p.max_len);
> >>> dma_sync_single_range_for_device(pool->p.dev, dma_addr,
> >>> @@ -375,6 +383,12 @@ static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
> >>> {
> >>> dma_addr_t dma;
> >>>
> >>> + if (page_is_page_pool_iov(page)) {
> >>> + /* page_pool_iovs are already mapped */
> >>> + DEBUG_NET_WARN_ON_ONCE(true);
> >>> + return true;
> >>> + }
> >>> +
> >>> /* Setup DMA mapping: use 'struct page' area for storing DMA-addr
> >>> * since dma_addr_t can be either 32 or 64 bits and does not always fit
> >>> * into page private data (i.e 32bit cpu with 64bit DMA caps)
> >>> @@ -398,14 +412,24 @@ static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
> >>> static void page_pool_set_pp_info(struct page_pool *pool,
> >>> struct page *page)
> >>> {
> >>> - page->pp = pool;
> >>> - page->pp_magic |= PP_SIGNATURE;
> >>> + if (!page_is_page_pool_iov(page)) {
> >>> + page->pp = pool;
> >>> + page->pp_magic |= PP_SIGNATURE;
> >>> + } else {
> >>> + page_to_page_pool_iov(page)->pp = pool;
> >>> + }
> >>> +
> >>> if (pool->p.init_callback)
> >>> pool->p.init_callback(page, pool->p.init_arg);
> >>> }
> >>>
> >>> static void page_pool_clear_pp_info(struct page *page)
> >>> {
> >>> + if (page_is_page_pool_iov(page)) {
> >>> + page_to_page_pool_iov(page)->pp = NULL;
> >>> + return;
> >>> + }
> >>> +
> >>> page->pp_magic = 0;
> >>> page->pp = NULL;
> >>> }
> >>> @@ -615,7 +639,7 @@ static bool page_pool_recycle_in_cache(struct page *page,
> >>> return false;
> >>> }
> >>>
> >>> - /* Caller MUST have verified/know (page_ref_count(page) == 1) */
> >>> + /* Caller MUST have verified/know (page_pool_page_ref_count(page) == 1) */
> >>> pool->alloc.cache[pool->alloc.count++] = page;
> >>> recycle_stat_inc(pool, cached);
> >>> return true;
> >>> @@ -638,9 +662,10 @@ __page_pool_put_page(struct page_pool *pool, struct page *page,
> >>> * refcnt == 1 means page_pool owns page, and can recycle it.
> >>> *
> >>> * page is NOT reusable when allocated when system is under
> >>> - * some pressure. (page_is_pfmemalloc)
> >>> + * some pressure. (page_pool_page_is_pfmemalloc)
> >>> */
> >>> - if (likely(page_ref_count(page) == 1 && !page_is_pfmemalloc(page))) {
> >>> + if (likely(page_pool_page_ref_count(page) == 1 &&
> >>> + !page_pool_page_is_pfmemalloc(page))) {
> >>> /* Read barrier done in page_ref_count / READ_ONCE */
> >>>
> >>> if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
> >>> @@ -741,7 +766,8 @@ static struct page *page_pool_drain_frag(struct page_pool *pool,
> >>> if (likely(page_pool_defrag_page(page, drain_count)))
> >>> return NULL;
> >>>
> >>> - if (page_ref_count(page) == 1 && !page_is_pfmemalloc(page)) {
> >>> + if (page_pool_page_ref_count(page) == 1 &&
> >>> + !page_pool_page_is_pfmemalloc(page)) {
> >>> if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
> >>> page_pool_dma_sync_for_device(pool, page, -1);
> >>>
> >>> @@ -818,9 +844,9 @@ static void page_pool_empty_ring(struct page_pool *pool)
> >>> /* Empty recycle ring */
> >>> while ((page = ptr_ring_consume_bh(&pool->ring))) {
> >>> /* Verify the refcnt invariant of cached pages */
> >>> - if (!(page_ref_count(page) == 1))
> >>> + if (!(page_pool_page_ref_count(page) == 1))
> >>> pr_crit("%s() page_pool refcnt %d violation\n",
> >>> - __func__, page_ref_count(page));
> >>> + __func__, page_pool_page_ref_count(page));
> >>>
> >>> page_pool_return_page(pool, page);
> >>> }
> >>> @@ -977,19 +1003,24 @@ bool page_pool_return_skb_page(struct page *page, bool napi_safe)
> >>> struct page_pool *pp;
> >>> bool allow_direct;
> >>>
> >>> - page = compound_head(page);
> >>> + if (!page_is_page_pool_iov(page)) {
> >>> + page = compound_head(page);
> >>>
> >>> - /* page->pp_magic is OR'ed with PP_SIGNATURE after the allocation
> >>> - * in order to preserve any existing bits, such as bit 0 for the
> >>> - * head page of compound page and bit 1 for pfmemalloc page, so
> >>> - * mask those bits for freeing side when doing below checking,
> >>> - * and page_is_pfmemalloc() is checked in __page_pool_put_page()
> >>> - * to avoid recycling the pfmemalloc page.
> >>> - */
> >>> - if (unlikely((page->pp_magic & ~0x3UL) != PP_SIGNATURE))
> >>> - return false;
> >>> + /* page->pp_magic is OR'ed with PP_SIGNATURE after the
> >>> + * allocation in order to preserve any existing bits, such as
> >>> + * bit 0 for the head page of compound page and bit 1 for
> >>> + * pfmemalloc page, so mask those bits for freeing side when
> >>> + * doing below checking, and page_pool_page_is_pfmemalloc() is
> >>> + * checked in __page_pool_put_page() to avoid recycling the
> >>> + * pfmemalloc page.
> >>> + */
> >>> + if (unlikely((page->pp_magic & ~0x3UL) != PP_SIGNATURE))
> >>> + return false;
> >>>
> >>> - pp = page->pp;
> >>> + pp = page->pp;
> >>> + } else {
> >>> + pp = page_to_page_pool_iov(page)->pp;
> >>> + }
> >>>
> >>> /* Allow direct recycle if we have reasons to believe that we are
> >>> * in the same context as the consumer would run, so there's
> >>> @@ -1273,9 +1304,9 @@ static bool mp_huge_busy(struct mp_huge *hu, unsigned int idx)
> >>>
> >>> for (j = 0; j < (1 << MP_HUGE_ORDER); j++) {
> >>> page = hu->page[idx] + j;
> >>> - if (page_ref_count(page) != 1) {
> >>> + if (page_pool_page_ref_count(page) != 1) {
> >>> pr_warn("Page with ref count %d at %u, %u. Can't safely destory, leaking memory!\n",
> >>> - page_ref_count(page), idx, j);
> >>> + page_pool_page_ref_count(page), idx, j);
> >>> return true;
> >>> }
> >>> }
> >>> @@ -1330,7 +1361,7 @@ static struct page *mp_huge_alloc_pages(struct page_pool *pool, gfp_t gfp)
> >>> continue;
> >>>
> >>> if ((page->pp_magic & ~0x3UL) == PP_SIGNATURE ||
> >>> - page_ref_count(page) != 1) {
> >>> + page_pool_page_ref_count(page) != 1) {
> >>> atomic_inc(&mp_huge_ins_b);
> >>> continue;
> >>> }
> >>> @@ -1458,9 +1489,9 @@ static void mp_huge_1g_destroy(struct page_pool *pool)
> >>> free = true;
> >>> for (i = 0; i < MP_HUGE_1G_CNT; i++) {
> >>> page = hu->page + i;
> >>> - if (page_ref_count(page) != 1) {
> >>> + if (page_pool_page_ref_count(page) != 1) {
> >>> pr_warn("Page with ref count %d at %u. Can't safely destory, leaking memory!\n",
> >>> - page_ref_count(page), i);
> >>> + page_pool_page_ref_count(page), i);
> >>> free = false;
> >>> break;
> >>> }
> >>> @@ -1489,7 +1520,7 @@ static struct page *mp_huge_1g_alloc_pages(struct page_pool *pool, gfp_t gfp)
> >>> page = hu->page + page_i;
> >>>
> >>> if ((page->pp_magic & ~0x3UL) == PP_SIGNATURE ||
> >>> - page_ref_count(page) != 1) {
> >>> + page_pool_page_ref_count(page) != 1) {
> >>> atomic_inc(&mp_huge_ins_b);
> >>> continue;
> >>> }
> >>> --
> >>> 2.41.0.640.ga95def55d0-goog
> >>>
> >>
> >
> >
> > --
> > Thanks,
> > Mina
> >
>
--
Thanks,
Mina
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