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    SubjectRe: [RFC PATCH v3 07/12] page-pool: device memory support
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    Date
    On Sun, 2023-11-05 at 18:44 -0800, 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.
    >
    > In areas where struct page* is dereferenced, add a check for special
    > handling of page_pool_iov.
    >
    > Signed-off-by: Mina Almasry <almasrymina@google.com>
    >
    > ---
    > include/net/page_pool/helpers.h | 74 ++++++++++++++++++++++++++++++++-
    > net/core/page_pool.c | 63 ++++++++++++++++++++--------
    > 2 files changed, 118 insertions(+), 19 deletions(-)
    >
    > diff --git a/include/net/page_pool/helpers.h b/include/net/page_pool/helpers.h
    > index b93243c2a640..08f1a2cc70d2 100644
    > --- a/include/net/page_pool/helpers.h
    > +++ b/include/net/page_pool/helpers.h
    > @@ -151,6 +151,64 @@ 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;
    > +}
    > +
    > /**
    > * page_pool_dev_alloc_pages() - allocate a page.
    > * @pool: pool from which to allocate
    > @@ -301,6 +359,9 @@ 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:
    > * 1. 'n == 1': no need to actually overwrite it.
    > @@ -431,7 +492,12 @@ static inline void page_pool_free_va(struct page_pool *pool, void *va,
    > */
    > 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));

    Should the above conditional be guarded by the page_pool_mem_providers
    static key? this looks like fast-path. Same question for the refcount
    helper above.

    Minor nit: possibly cache 'page_is_page_pool_iov(page)' to make the
    code more readable.

    > +
    > + ret = page->dma_addr;
    >
    > if (PAGE_POOL_32BIT_ARCH_WITH_64BIT_DMA)
    > ret <<= PAGE_SHIFT;
    > @@ -441,6 +507,12 @@ static inline dma_addr_t page_pool_get_dma_addr(struct page *page)
    >
    > static inline bool 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 false;
    > + }

    Quickly skimming over the page_pool_code it looks like
    page_pool_set_dma_addr() usage is guarded by the PP_FLAG_DMA_MAP page
    pool flag. Could the device mem provider enforce such flag being
    cleared on the page pool?

    > +
    > if (PAGE_POOL_32BIT_ARCH_WITH_64BIT_DMA) {
    > page->dma_addr = addr >> PAGE_SHIFT;
    >
    > diff --git a/net/core/page_pool.c b/net/core/page_pool.c
    > index 138ddea0b28f..d211996d423b 100644
    > --- a/net/core/page_pool.cnn
    > +++ b/net/core/page_pool.c
    > @@ -317,7 +317,7 @@ 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;
    > @@ -362,7 +362,15 @@ 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;
    > + }

    Similar to the above point, mutatis mutandis.

    > +
    > + 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,
    > @@ -374,6 +382,12 @@ 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;
    > + }

    Ditto.

    Cheers,

    Paolo

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