netdev - Re: [PATCH resend mm,net-next 1/3] mm: Refactor insert

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Date:   Wed, 12 Feb 2020 18:41:15 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Arjun Roy <arjunroy.kdev@...il.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, linux-mm@...ck.org,
        arjunroy@...gle.com, Eric Dumazet <edumazet@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>
Subject: Re: [PATCH resend mm,net-next 1/3] mm: Refactor insert_page to
 prepare for batched-lock insert.

On Mon, 27 Jan 2020 18:59:56 -0800 Arjun Roy <arjunroy.kdev@...il.com> wrote:

> Add helper methods for vm_insert_page()/insert_page() to prepare for
> vm_insert_pages(), which batch-inserts pages to reduce spinlock
> operations when inserting multiple consecutive pages into the user
> page table.
> 
> The intention of this patch-set is to reduce atomic ops for
> tcp zerocopy receives, which normally hits the same spinlock multiple
> times consecutively.

I tweaked this a bit for the addition of page_has_type() to
insert_page().  Please check.



From: Arjun Roy <arjunroy.kdev@...il.com>
Subject: mm: Refactor insert_page to prepare for batched-lock insert.

From: Arjun Roy <arjunroy@...gle.com>

Add helper methods for vm_insert_page()/insert_page() to prepare for
vm_insert_pages(), which batch-inserts pages to reduce spinlock
operations when inserting multiple consecutive pages into the user
page table.

The intention of this patch-set is to reduce atomic ops for
tcp zerocopy receives, which normally hits the same spinlock multiple
times consecutively.

Link: http://lkml.kernel.org/r/20200128025958.43490-1-arjunroy.kdev@gmail.com
Signed-off-by: Arjun Roy <arjunroy@...gle.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil@...gle.com>

Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 mm/memory.c |   39 ++++++++++++++++++++++++---------------
 1 file changed, 24 insertions(+), 15 deletions(-)

--- a/mm/memory.c~mm-refactor-insert_page-to-prepare-for-batched-lock-insert
+++ a/mm/memory.c
@@ -1430,6 +1430,27 @@ pte_t *__get_locked_pte(struct mm_struct
 	return pte_alloc_map_lock(mm, pmd, addr, ptl);
 }
 
+static int validate_page_before_insert(struct page *page)
+{
+	if (PageAnon(page) || PageSlab(page) || page_has_type(page))
+		return -EINVAL;
+	flush_dcache_page(page);
+	return 0;
+}
+
+static int insert_page_into_pte_locked(struct mm_struct *mm, pte_t *pte,
+			unsigned long addr, struct page *page, pgprot_t prot)
+{
+	if (!pte_none(*pte))
+		return -EBUSY;
+	/* Ok, finally just insert the thing.. */
+	get_page(page);
+	inc_mm_counter_fast(mm, mm_counter_file(page));
+	page_add_file_rmap(page, false);
+	set_pte_at(mm, addr, pte, mk_pte(page, prot));
+	return 0;
+}
+
 /*
  * This is the old fallback for page remapping.
  *
@@ -1445,26 +1466,14 @@ static int insert_page(struct vm_area_st
 	pte_t *pte;
 	spinlock_t *ptl;
 
-	retval = -EINVAL;
-	if (PageAnon(page) || PageSlab(page) || page_has_type(page))
+	retval = validate_page_before_insert(page);
+	if (retval)
 		goto out;
 	retval = -ENOMEM;
-	flush_dcache_page(page);
 	pte = get_locked_pte(mm, addr, &ptl);
 	if (!pte)
 		goto out;
-	retval = -EBUSY;
-	if (!pte_none(*pte))
-		goto out_unlock;
-
-	/* Ok, finally just insert the thing.. */
-	get_page(page);
-	inc_mm_counter_fast(mm, mm_counter_file(page));
-	page_add_file_rmap(page, false);
-	set_pte_at(mm, addr, pte, mk_pte(page, prot));
-
-	retval = 0;
-out_unlock:
+	retval = insert_page_into_pte_locked(mm, pte, addr, page, prot);
 	pte_unmap_unlock(pte, ptl);
 out:
 	return retval;
_