linux-kernel - Re: [PATCH] mm/hugetlb: avoid looping to the same hugepage if !pages and !vmas

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Date:   Thu, 29 Aug 2019 04:54:57 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     zhigang lu <luzhigang001@...il.com>
Cc:     mike.kravetz@...cle.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, tonnylu@...cent.com,
        hzhongzhang@...cent.com, knightzhang@...cent.com
Subject: Re: [PATCH] mm/hugetlb: avoid looping to the same hugepage if !pages
 and !vmas

On Thu, Aug 29, 2019 at 07:37:22PM +0800, zhigang lu wrote:
> This change greatly decrease the time of mmaping a file in hugetlbfs.
> With MAP_POPULATE flag, it takes about 50 milliseconds to mmap a
> existing 128GB file in hugetlbfs. With this change, it takes less
> then 1 millisecond.

You're going to need to find a new way of sending patches; this patch is
mangled by your mail system.

> @@ -4391,6 +4391,17 @@ long follow_hugetlb_page(struct mm_struct *mm,
> struct vm_area_struct *vma,
>   break;
>   }
>   }
> +
> + if (!pages && !vmas && !pfn_offset &&
> +     (vaddr + huge_page_size(h) < vma->vm_end) &&
> +     (remainder >= pages_per_huge_page(h))) {
> + vaddr += huge_page_size(h);
> + remainder -= pages_per_huge_page(h);
> + i += pages_per_huge_page(h);
> + spin_unlock(ptl);
> + continue;
> + }

The concept seems good to me.  The description above could do with some
better explanation though.