From: Alexander Duyck <alexander.duyck@gmail.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: linux-mm <linux-mm@kvack.org>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH 2/6] mm: Optimise find_subpage for !THP
Date: Tue, 3 Mar 2020 13:28:13 -0800 [thread overview]
Message-ID: <CAKgT0UexbGe8P=DG23BWCRfnpDK40pCVU+DVqwP8BL-oktijAA@mail.gmail.com> (raw)
In-Reply-To: <20200303041125.19358-3-willy@infradead.org>
On Mon, Mar 2, 2020 at 8:11 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
>
> If THP is disabled, find_subpage can become a no-op.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
> include/linux/pagemap.h | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index b4ea3a5d00e5..8785f60b05f8 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -333,14 +333,19 @@ static inline struct page *grab_cache_page_nowait(struct address_space *mapping,
> mapping_gfp_mask(mapping));
> }
>
> -static inline struct page *find_subpage(struct page *page, pgoff_t offset)
> +/*
> + * Given the page we found in the page cache, return the page corresponding
> + * to this offset in the file
> + */
> +static inline struct page *find_subpage(struct page *head, pgoff_t offset)
> {
> - if (PageHuge(page))
> - return page;
> + /* HugeTLBfs wants the head page regardless */
> + if (PageHuge(head))
> + return head;
>
> - VM_BUG_ON_PAGE(PageTail(page), page);
> + VM_BUG_ON_PAGE(PageTail(head), head);
Is there any specific reason for renaming page to head? Just wondering
since it adds some noise to the patch that wasn't really called out in
the patch description. From what I can tell none of the changes above
this point have any explanation to them in the patch description, and
until I noticed the change below I thought maybe you had the wrong
patch description for this patch.
> - return page + (offset & (compound_nr(page) - 1));
> + return head + (offset & (hpage_nr_pages(head) - 1));
> }
So the patch description refers to this line here, correct?
One thing I am noticing is that it looks like the VM_BUG_ON_PAGE is
now redundant. If I am not not mistaken hpage_nr_pages will call
PageTransHuge which also performs the same check. So do you still need
the VM_BUG_ON_PAGE call in this function?
next prev parent reply other threads:[~2020-03-03 21:28 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-03 4:11 [PATCH 0/6] Misc MM patches Matthew Wilcox
2020-03-03 4:11 ` [PATCH 1/6] mm: Use vm_fault error code directly Matthew Wilcox
2020-03-03 4:11 ` [PATCH 2/6] mm: Optimise find_subpage for !THP Matthew Wilcox
2020-03-03 21:28 ` Alexander Duyck [this message]
2020-03-03 21:47 ` Matthew Wilcox
2020-03-05 9:54 ` William Kucharski
2020-03-03 4:11 ` [PATCH 3/6] mm: Remove CONFIG_TRANSPARENT_HUGE_PAGECACHE Matthew Wilcox
2020-03-03 21:52 ` Alexander Duyck
2020-03-03 22:34 ` Matthew Wilcox
2020-03-03 22:54 ` Alexander Duyck
2020-03-04 2:06 ` Matthew Wilcox
2020-03-03 4:11 ` [PATCH 4/6] mm: Use VM_BUG_ON_PAGE in clear_page_dirty_for_io Matthew Wilcox
2020-03-03 4:11 ` [PATCH 5/6] mm: Unexport find_get_entry Matthew Wilcox
2020-03-03 4:11 ` [PATCH 6/6] mm: Rewrite pagecache_get_page documentation Matthew Wilcox
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