Messages in this thread Patch in this message | | | Date | Sun, 3 Jun 2007 21:05:08 +0800 | From | Fengguang Wu <> | Subject | Re: [PATCH] sendfile removal |
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On Sat, Jun 02, 2007 at 08:40:04AM -0700, Linus Torvalds wrote: > On Sat, 2 Jun 2007, Jens Axboe wrote: > Your suggested: > > > if ((flags & SPLICE_F_NONBLOCK) && spd.nr_pages) { > > if (TestSetPageLocked(page)) > > break; > > } else > > lock_page(page); > > > > should do that - always block for the first page and potentially return > > a partial results for the remaining pages that read-ahead kicked into > > gear. > > would work, but I suspect that for a server, returning EAGAIN once is > actually the best option - if it has a select() loop, and something else > is running, the "return EAGAIN once" actually makes tons of sense (it > would basically boil down to the kernel effectively saying "ok, try > anything else you might have pending in your queues first, if you get back > to me, I'll block then").
May be we can settle with "return EAGAIN once" for *all* possible waits, including I/O submitted by others:
if ((flags & SPLICE_F_NONBLOCK) && TestSetPageLocked(page) && in->f_ra.prev_index != index) break; else lock_page(page);
However, the upper layer generic_file_splice_read() may keep on calling __generic_file_splice_read(), so we need more code to stop it with flag SPLICE_INTERNAL_WILLBLOCK:
--- (not tested yet; still not sure if it's the best solution.)
In non-block splicing, return EAGAIN once for all possible I/O waits.
It works by checking (ra.prev_index != index) in __generic_file_splice_read(). Another reader on the same fd will at worst cause a few more splice syscalls.
If keep calling generic_file_splice_read() in non-block mode, it will return partial data before the first hole; then return EAGAIN at second call; at last it will block on the I/O page.
Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn> --- fs/splice.c | 38 ++++++++++++++++++++++-------------- include/linux/pipe_fs_i.h | 2 + 2 files changed, 26 insertions(+), 14 deletions(-)
--- linux-2.6.22-rc3-mm1.orig/fs/splice.c +++ linux-2.6.22-rc3-mm1/fs/splice.c @@ -264,10 +264,11 @@ static ssize_t splice_to_pipe(struct pip static int __generic_file_splice_read(struct file *in, loff_t *ppos, struct pipe_inode_info *pipe, size_t len, - unsigned int flags) + unsigned int *flags) { struct address_space *mapping = in->f_mapping; unsigned int loff, nr_pages; + unsigned int first_hole; struct page *pages[PIPE_BUFFERS]; struct partial_page partial[PIPE_BUFFERS]; struct page *page; @@ -278,7 +279,7 @@ __generic_file_splice_read(struct file * struct splice_pipe_desc spd = { .pages = pages, .partial = partial, - .flags = flags, + .flags = *flags, .ops = &page_cache_pipe_buf_ops, }; @@ -299,12 +300,17 @@ __generic_file_splice_read(struct file * * Lookup the (hopefully) full range of pages we need. */ spd.nr_pages = find_get_pages_contig(mapping, index, nr_pages, pages); + first_hole = spd.nr_pages; + index += spd.nr_pages; /* * If find_get_pages_contig() returned fewer pages than we needed, - * allocate the rest. + * readahead/allocate the rest. */ - index += spd.nr_pages; + if (spd.nr_pages < nr_pages) + page_cache_readahead_ondemand(mapping, &in->f_ra, in, + NULL, index, nr_pages - spd.nr_pages); + while (spd.nr_pages < nr_pages) { /* * Page could be there, find_get_pages_contig() breaks on @@ -312,9 +318,6 @@ __generic_file_splice_read(struct file * */ page = find_get_page(mapping, index); if (!page) { - page_cache_readahead_ondemand(mapping, &in->f_ra, in, - NULL, index, nr_pages - spd.nr_pages); - /* * page didn't exist, allocate one. */ @@ -369,13 +372,13 @@ __generic_file_splice_read(struct file * */ if (!PageUptodate(page)) { /* - * If in nonblock mode then dont block on waiting - * for an in-flight io page + * In non-block mode, only block at the second try. */ - if (flags & SPLICE_F_NONBLOCK) { - if (TestSetPageLocked(page)) - break; - } else + if ((*flags & SPLICE_F_NONBLOCK) && + TestSetPageLocked(page) && + in->f_ra.prev_index != index) + break; + else lock_page(page); /* @@ -454,6 +457,10 @@ fill_it: page_cache_release(pages[page_nr++]); in->f_ra.prev_index = index; + if ((*flags & SPLICE_F_NONBLOCK) && (spd.nr_pages > first_hole)) { + *flags |= SPLICE_INTERNAL_WILLBLOCK; + spd.nr_pages = first_hole; + } if (spd.nr_pages) return splice_to_pipe(pipe, &spd); @@ -480,7 +487,7 @@ ssize_t generic_file_splice_read(struct spliced = 0; while (len) { - ret = __generic_file_splice_read(in, ppos, pipe, len, flags); + ret = __generic_file_splice_read(in, ppos, pipe, len, &flags); if (ret < 0) break; @@ -496,6 +503,9 @@ ssize_t generic_file_splice_read(struct *ppos += ret; len -= ret; spliced += ret; + + if (flags & SPLICE_INTERNAL_WILLBLOCK) + break; } if (spliced) --- linux-2.6.22-rc3-mm1.orig/include/linux/pipe_fs_i.h +++ linux-2.6.22-rc3-mm1/include/linux/pipe_fs_i.h @@ -82,6 +82,8 @@ int generic_pipe_buf_steal(struct pipe_i #define SPLICE_F_MORE (0x04) /* expect more data */ #define SPLICE_F_GIFT (0x08) /* pages passed in are a gift */ +#define SPLICE_INTERNAL_WILLBLOCK (0x100) /* read on next page will block */ + /* * Passed to the actors */ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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