* [PATCH mm,net-next 2/3] mm: Add vm_insert_pages().
2020-01-11 0:28 [PATCH mm,net-next 1/3] mm: Refactor insert_page to prepare for batched-lock insert Arjun Roy
@ 2020-01-11 0:28 ` Arjun Roy
2020-01-11 0:28 ` [PATCH mm,net-next 3/3] net-zerocopy: Use vm_insert_pages() for tcp rcv zerocopy Arjun Roy
1 sibling, 0 replies; 3+ messages in thread
From: Arjun Roy @ 2020-01-11 0:28 UTC (permalink / raw)
To: davem, netdev, akpm, linux-mm
Cc: arjunroy, Arjun Roy, Eric Dumazet, Soheil Hassas Yeganeh
Add the ability to insert multiple pages at once to a user VM with
lower PTE spinlock operations.
The intention of this patch-set is to reduce atomic ops for
tcp zerocopy receives, which normally hits the same spinlock multiple
times consecutively.
Signed-off-by: Arjun Roy <arjunroy.kdev@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
---
include/linux/mm.h | 2 +
mm/memory.c | 111 ++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 111 insertions(+), 2 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 29c928ba6b42..a3ac40fbe8fd 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2563,6 +2563,8 @@ struct vm_area_struct *find_extend_vma(struct mm_struct *, unsigned long addr);
int remap_pfn_range(struct vm_area_struct *, unsigned long addr,
unsigned long pfn, unsigned long size, pgprot_t);
int vm_insert_page(struct vm_area_struct *, unsigned long addr, struct page *);
+int vm_insert_pages(struct vm_area_struct *vma, unsigned long addr,
+ struct page **pages, unsigned long *num);
int vm_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
unsigned long pfn);
int vm_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr,
diff --git a/mm/memory.c b/mm/memory.c
index 7e23a9275386..1655c5feaf32 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1670,8 +1670,7 @@ int zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
}
EXPORT_SYMBOL_GPL(zap_vma_ptes);
-pte_t *__get_locked_pte(struct mm_struct *mm, unsigned long addr,
- spinlock_t **ptl)
+static pmd_t *walk_to_pmd(struct mm_struct *mm, unsigned long addr)
{
pgd_t *pgd;
p4d_t *p4d;
@@ -1690,6 +1689,16 @@ pte_t *__get_locked_pte(struct mm_struct *mm, unsigned long addr,
return NULL;
VM_BUG_ON(pmd_trans_huge(*pmd));
+ return pmd;
+}
+
+pte_t *__get_locked_pte(struct mm_struct *mm, unsigned long addr,
+ spinlock_t **ptl)
+{
+ pmd_t *pmd = walk_to_pmd(mm, addr);
+
+ if (!pmd)
+ return NULL;
return pte_alloc_map_lock(mm, pmd, addr, ptl);
}
@@ -1714,6 +1723,15 @@ static int insert_page_into_pte_locked(struct mm_struct *mm, pte_t *pte,
return 0;
}
+static int insert_page_in_batch_locked(struct mm_struct *mm, pmd_t *pmd,
+ unsigned long addr, struct page *page, pgprot_t prot)
+{
+ const int err = validate_page_before_insert(page);
+
+ return err ? err : insert_page_into_pte_locked(
+ mm, pte_offset_map(pmd, addr), addr, page, prot);
+}
+
/*
* This is the old fallback for page remapping.
*
@@ -1742,6 +1760,95 @@ static int insert_page(struct vm_area_struct *vma, unsigned long addr,
return retval;
}
+/* insert_pages() amortizes the cost of spinlock operations
+ * when inserting pages in a loop.
+ */
+static int insert_pages(struct vm_area_struct *vma, unsigned long addr,
+ struct page **pages, unsigned long *num, pgprot_t prot)
+{
+ pmd_t *pmd = NULL;
+ spinlock_t *pte_lock = NULL;
+ struct mm_struct *const mm = vma->vm_mm;
+ unsigned long curr_page_idx = 0;
+ unsigned long remaining_pages_total = *num;
+ unsigned long pages_to_write_in_pmd;
+ int ret;
+more:
+ ret = -EFAULT;
+ pmd = walk_to_pmd(mm, addr);
+ if (!pmd)
+ goto out;
+
+ pages_to_write_in_pmd = min_t(unsigned long,
+ remaining_pages_total, PTRS_PER_PTE - pte_index(addr));
+
+ /* Allocate the PTE if necessary; takes PMD lock once only. */
+ ret = -ENOMEM;
+ if (pte_alloc(mm, pmd, addr))
+ goto out;
+ pte_lock = pte_lockptr(mm, pmd);
+
+ while (pages_to_write_in_pmd) {
+ int pte_idx = 0;
+ const int batch_size = min_t(int, pages_to_write_in_pmd, 8);
+
+ spin_lock(pte_lock);
+ for (; pte_idx < batch_size; ++pte_idx) {
+ int err = insert_page_in_batch_locked(mm, pmd,
+ addr, pages[curr_page_idx], prot);
+ if (unlikely(err)) {
+ spin_unlock(pte_lock);
+ ret = err;
+ remaining_pages_total -= pte_idx;
+ goto out;
+ }
+ addr += PAGE_SIZE;
+ ++curr_page_idx;
+ }
+ spin_unlock(pte_lock);
+ pages_to_write_in_pmd -= batch_size;
+ remaining_pages_total -= batch_size;
+ }
+ if (remaining_pages_total)
+ goto more;
+ ret = 0;
+out:
+ *num = remaining_pages_total;
+ return ret;
+}
+
+/**
+ * vm_insert_pages - insert multiple pages into user vma, batching the pmd lock.
+ * @vma: user vma to map to
+ * @addr: target start user address of these pages
+ * @pages: source kernel pages
+ * @num: in: number of pages to map. out: number of pages that were *not*
+ * mapped. (0 means all pages were successfully mapped).
+ *
+ * Preferred over vm_insert_page() when inserting multiple pages.
+ *
+ * In case of error, we may have mapped a subset of the provided
+ * pages. It is the caller's responsibility to account for this case.
+ *
+ * The same restrictions apply as in vm_insert_page().
+ */
+int vm_insert_pages(struct vm_area_struct *vma, unsigned long addr,
+ struct page **pages, unsigned long *num)
+{
+ const unsigned long end_addr = addr + (*num * PAGE_SIZE) - 1;
+
+ if (addr < vma->vm_start || end_addr >= vma->vm_end)
+ return -EFAULT;
+ if (!(vma->vm_flags & VM_MIXEDMAP)) {
+ BUG_ON(down_read_trylock(&vma->vm_mm->mmap_sem));
+ BUG_ON(vma->vm_flags & VM_PFNMAP);
+ vma->vm_flags |= VM_MIXEDMAP;
+ }
+ /* Defer page refcount checking till we're about to map that page. */
+ return insert_pages(vma, addr, pages, num, vma->vm_page_prot);
+}
+EXPORT_SYMBOL(vm_insert_pages);
+
/**
* vm_insert_page - insert single page into user vma
* @vma: user vma to map to
--
2.25.0.rc1.283.g88dfdc4193-goog
^ permalink raw reply related [flat|nested] 3+ messages in thread* [PATCH mm,net-next 3/3] net-zerocopy: Use vm_insert_pages() for tcp rcv zerocopy.
2020-01-11 0:28 [PATCH mm,net-next 1/3] mm: Refactor insert_page to prepare for batched-lock insert Arjun Roy
2020-01-11 0:28 ` [PATCH mm,net-next 2/3] mm: Add vm_insert_pages() Arjun Roy
@ 2020-01-11 0:28 ` Arjun Roy
1 sibling, 0 replies; 3+ messages in thread
From: Arjun Roy @ 2020-01-11 0:28 UTC (permalink / raw)
To: davem, netdev, akpm, linux-mm
Cc: arjunroy, Arjun Roy, Eric Dumazet, Soheil Hassas Yeganeh
Use vm_insert_pages() for tcp receive zerocopy. Spin lock cycles
(as reported by perf) drop from a couple of percentage points
to a fraction of a percent. This results in a roughly 6% increase in
efficiency, measured roughly as zerocopy receive count divided by CPU
utilization.
The intention of this patch-set is to reduce atomic ops for
tcp zerocopy receives, which normally hits the same spinlock multiple
times consecutively.
Signed-off-by: Arjun Roy <arjunroy.kdev@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
---
net/ipv4/tcp.c | 67 +++++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 61 insertions(+), 6 deletions(-)
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 34490d972758..52f96c3ceab3 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1861,14 +1861,48 @@ int tcp_mmap(struct file *file, struct socket *sock,
}
EXPORT_SYMBOL(tcp_mmap);
+static int tcp_zerocopy_vm_insert_batch(struct vm_area_struct *vma,
+ struct page **pages,
+ unsigned long pages_to_map,
+ unsigned long *insert_addr,
+ u32 *length_with_pending,
+ u32 *seq,
+ struct tcp_zerocopy_receive *zc)
+{
+ unsigned long pages_remaining = pages_to_map;
+ int bytes_mapped;
+ int ret;
+
+ ret = vm_insert_pages(vma, *insert_addr, pages, &pages_remaining);
+ bytes_mapped = PAGE_SIZE * (pages_to_map - pages_remaining);
+ /* Even if vm_insert_pages fails, it may have partially succeeded in
+ * mapping (some but not all of the pages).
+ */
+ *seq += bytes_mapped;
+ *insert_addr += bytes_mapped;
+ if (ret) {
+ /* But if vm_insert_pages did fail, we have to unroll some state
+ * we speculatively touched before.
+ */
+ const int bytes_not_mapped = PAGE_SIZE * pages_remaining;
+ *length_with_pending -= bytes_not_mapped;
+ zc->recv_skip_hint += bytes_not_mapped;
+ }
+ return ret;
+}
+
static int tcp_zerocopy_receive(struct sock *sk,
struct tcp_zerocopy_receive *zc)
{
unsigned long address = (unsigned long)zc->address;
u32 length = 0, seq, offset, zap_len;
+ #define PAGE_BATCH_SIZE 8
+ struct page *pages[PAGE_BATCH_SIZE];
const skb_frag_t *frags = NULL;
struct vm_area_struct *vma;
struct sk_buff *skb = NULL;
+ unsigned long pg_idx = 0;
+ unsigned long curr_addr;
struct tcp_sock *tp;
int inq;
int ret;
@@ -1901,15 +1935,26 @@ static int tcp_zerocopy_receive(struct sock *sk,
zc->recv_skip_hint = zc->length;
}
ret = 0;
+ curr_addr = address;
while (length + PAGE_SIZE <= zc->length) {
if (zc->recv_skip_hint < PAGE_SIZE) {
+ /* If we're here, finish the current batch. */
+ if (pg_idx) {
+ ret = tcp_zerocopy_vm_insert_batch(vma, pages,
+ pg_idx,
+ &curr_addr,
+ &length,
+ &seq, zc);
+ if (ret)
+ goto out;
+ pg_idx = 0;
+ }
if (skb) {
skb = skb->next;
offset = seq - TCP_SKB_CB(skb)->seq;
} else {
skb = tcp_recv_skb(sk, seq, &offset);
}
-
zc->recv_skip_hint = skb->len - offset;
offset -= skb_headlen(skb);
if ((int)offset < 0 || skb_has_frag_list(skb))
@@ -1933,14 +1978,24 @@ static int tcp_zerocopy_receive(struct sock *sk,
zc->recv_skip_hint -= remaining;
break;
}
- ret = vm_insert_page(vma, address + length,
- skb_frag_page(frags));
- if (ret)
- break;
+ pages[pg_idx] = skb_frag_page(frags);
+ pg_idx++;
length += PAGE_SIZE;
- seq += PAGE_SIZE;
zc->recv_skip_hint -= PAGE_SIZE;
frags++;
+ if (pg_idx == PAGE_BATCH_SIZE) {
+ ret = tcp_zerocopy_vm_insert_batch(vma, pages, pg_idx,
+ &curr_addr, &length,
+ &seq, zc);
+ if (ret)
+ goto out;
+ pg_idx = 0;
+ }
+ }
+ if (pg_idx) {
+ ret = tcp_zerocopy_vm_insert_batch(vma, pages, pg_idx,
+ &curr_addr, &length, &seq,
+ zc);
}
out:
up_read(¤t->mm->mmap_sem);
--
2.25.0.rc1.283.g88dfdc4193-goog
^ permalink raw reply related [flat|nested] 3+ messages in thread