Jens Axboe <[email protected]> wrote:
>
> Actually it isn't so bad, how does this look?
>
> ...
>
> @@ -180,30 +181,48 @@ static int __generic_file_splice_read(st
> i = find_get_pages(mapping, index, nr_pages, pages);
>
> /*
> - * If not all pages were in the page-cache, we'll
> - * just assume that the rest haven't been read in,
> - * so we'll get the rest locked and start IO on
> - * them if we can..
> + * common case - we found all pages, kick it off
> */
> - while (i < nr_pages) {
> - struct page *page;
> - int error;
> -
> - page = find_or_create_page(mapping, index + i, GFP_USER);
> - if (!page)
> - break;
> + if (i == nr_pages)
> + goto splice_them;
The return value from find_get_pages() is "how many pages did I find" - it
doesn't tell us whether they were contiguous.
How about
if (i && (pages[i - 1]->index == index + i - 1))
<thinks>
So if we asked for N pages starting at index=10 and got
[11, 13]
i == 2
pages[i-1]->index == 13
index + i - 1 == 11.
So I think it's OK. Yeah, it has to be - any gap at all in the returned
page array will make pages[i-1]->index too big.
The one-at-a-time logic looks OK from a quick scan. Do we have logic in
there to check that we're not overrunning i_size? (See the pain
do_generic_mapping_read() goes through).
argh, readahead. Really we should be kicking the readahead engine in there
as well. That's fairly straightforward - see do_generic_mapping_read().
Also, the code here _might_ be able to use do_page_cache_readahead() just
to prepopulate the pages which you know you'll be needing. There are no
guarantees that the pages will still be there when you want them of course,
but it's a decent way of putting a block of pages into a single BIO and
speeding up the common case. But if the code is calling
page_cache_readahead() it won't need to do that.
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