[PATCH 1/1] UBUNTU: SAUCE: add tracing for user initiated readahead requests

[Stefan Bader]

On 07/29/2010 10:46 AM, Andy Whitcroft wrote:
> Track pages which undergo readahead and for each record which were
> actually consumed, via either read or faulted into a map.  This allows
> userspace readahead applications (such as ureadahead) to track which
> pages in core at the end of a boot are actually required and generate an
> optimal readahead pack.  It also allows pack adjustment and optimisation
> in parallel with readahead, allowing the pack to evolve to be accurate
> as userspace paths change.  The status of the pages are reported back via
> the mincore() call using a newly allocated bit.
> 
> Signed-off-by: Andy Whitcroft <apw at canonical.com>
> ---
>  include/linux/page-flags.h |    3 +++
>  mm/filemap.c               |    3 +++
>  mm/memory.c                |    7 ++++++-
>  mm/mincore.c               |    2 ++
>  mm/readahead.c             |    1 +
>  5 files changed, 15 insertions(+), 1 deletions(-)
> 
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 5b59f35..89dc94f 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -108,6 +108,7 @@ enum pageflags {
>  #ifdef CONFIG_MEMORY_FAILURE
>  	PG_hwpoison,		/* hardware poisoned page. Don't touch */
>  #endif
> +	PG_readaheadunused,	/* user oriented readahead as yet unused*/
>  	__NR_PAGEFLAGS,
>  
>  	/* Filesystems */
> @@ -239,6 +240,8 @@ PAGEFLAG(MappedToDisk, mappedtodisk)
>  PAGEFLAG(Reclaim, reclaim) TESTCLEARFLAG(Reclaim, reclaim)
>  PAGEFLAG(Readahead, reclaim)		/* Reminder to do async read-ahead */
>  
> +PAGEFLAG(ReadaheadUnused, readaheadunused)
> +
>  #ifdef CONFIG_HIGHMEM
>  /*
>   * Must use a macro here due to header dependency issues. page_zone() is not
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 20e5642..26e5e15 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1192,6 +1192,9 @@ int file_read_actor(read_descriptor_t *desc, struct page *page,
>  	if (size > count)
>  		size = count;
>  
> +	if (PageReadaheadUnused(page))
> +		ClearPageReadaheadUnused(page);
> +
>  	/*
>  	 * Faults on the destination of a read are common, so do it before
>  	 * taking the kmap.
> diff --git a/mm/memory.c b/mm/memory.c
> index 119b7cc..97ca21b 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2865,10 +2865,15 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma,
>  	else
>  		VM_BUG_ON(!PageLocked(vmf.page));
>  
> +	page = vmf.page;
> +
> +	/* Mark the page as used on fault. */
> +	if (PageReadaheadUnused(page))
> +		ClearPageReadaheadUnused(page);
> +
>  	/*
>  	 * Should we do an early C-O-W break?
>  	 */
> -	page = vmf.page;
>  	if (flags & FAULT_FLAG_WRITE) {
>  		if (!(vma->vm_flags & VM_SHARED)) {
>  			anon = 1;
> diff --git a/mm/mincore.c b/mm/mincore.c
> index 9ac42dc..a4e573a 100644
> --- a/mm/mincore.c
> +++ b/mm/mincore.c
> @@ -77,6 +77,8 @@ static unsigned char mincore_page(struct address_space *mapping, pgoff_t pgoff)
>  	page = find_get_page(mapping, pgoff);
>  	if (page) {
>  		present = PageUptodate(page);
> +		if (present)
> +			present |= (PageReadaheadUnused(page) << 7);
>  		page_cache_release(page);
>  	}
>  
> diff --git a/mm/readahead.c b/mm/readahead.c
> index 77506a2..6948b92 100644
> --- a/mm/readahead.c
> +++ b/mm/readahead.c
> @@ -181,6 +181,7 @@ __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
>  		list_add(&page->lru, &page_pool);
>  		if (page_idx == nr_to_read - lookahead_size)
>  			SetPageReadahead(page);
> +		SetPageReadaheadUnused(page);
>  		ret++;
>  	}
>  

I think it looks good. Just out of interest, the last hunk sounds a bit like it
only sets PageReadahead on one page while PageREadaheadUnused is set on all of
them. Which seems a bit odd.

-Stefan