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Message-ID: <alpine.LSU.2.00.1106091532370.2200@sister.anvils>
Date: Thu, 9 Jun 2011 15:33:32 -0700 (PDT)
From: Hugh Dickins <hughd@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH 2/7] tmpfs: refine shmem_file_splice_read
Tidy up shmem_file_splice_read():
Remove readahead: okay, we could implement shmem readahead on swap,
but have never done so before, swap being the slow exceptional path.
Use shmem_getpage() instead of find_or_create_page() plus ->readpage().
Remove several comments: sorry, I found them more distracting than
helpful, and this will not be the reference version of splice_read().
Signed-off-by: Hugh Dickins <hughd@...gle.com>
---
mm/shmem.c | 138 +++++++--------------------------------------------
1 file changed, 19 insertions(+), 119 deletions(-)
--- linux.orig/mm/shmem.c 2011-06-09 11:38:05.232808448 -0700
+++ linux/mm/shmem.c 2011-06-09 11:38:13.436849182 -0700
@@ -1850,6 +1850,7 @@ static ssize_t shmem_file_splice_read(st
unsigned int flags)
{
struct address_space *mapping = in->f_mapping;
+ struct inode *inode = mapping->host;
unsigned int loff, nr_pages, req_pages;
struct page *pages[PIPE_DEF_BUFFERS];
struct partial_page partial[PIPE_DEF_BUFFERS];
@@ -1865,7 +1866,7 @@ static ssize_t shmem_file_splice_read(st
.spd_release = spd_release_page,
};
- isize = i_size_read(in->f_mapping->host);
+ isize = i_size_read(inode);
if (unlikely(*ppos >= isize))
return 0;
@@ -1881,153 +1882,57 @@ static ssize_t shmem_file_splice_read(st
req_pages = (len + loff + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
nr_pages = min(req_pages, pipe->buffers);
- /*
- * Lookup the (hopefully) full range of pages we need.
- */
spd.nr_pages = find_get_pages_contig(mapping, index,
nr_pages, spd.pages);
index += spd.nr_pages;
-
- /*
- * If find_get_pages_contig() returned fewer pages than we needed,
- * readahead/allocate the rest and fill in the holes.
- */
- if (spd.nr_pages < nr_pages)
- page_cache_sync_readahead(mapping, &in->f_ra, in,
- index, req_pages - spd.nr_pages);
-
error = 0;
- while (spd.nr_pages < nr_pages) {
- /*
- * Page could be there, find_get_pages_contig() breaks on
- * the first hole.
- */
- page = find_get_page(mapping, index);
- if (!page) {
- /*
- * page didn't exist, allocate one.
- */
- page = page_cache_alloc_cold(mapping);
- if (!page)
- break;
-
- error = add_to_page_cache_lru(page, mapping, index,
- GFP_KERNEL);
- if (unlikely(error)) {
- page_cache_release(page);
- if (error == -EEXIST)
- continue;
- break;
- }
- /*
- * add_to_page_cache() locks the page, unlock it
- * to avoid convoluting the logic below even more.
- */
- unlock_page(page);
- }
+ while (spd.nr_pages < nr_pages) {
+ page = NULL;
+ error = shmem_getpage(inode, index, &page, SGP_CACHE, NULL);
+ if (error)
+ break;
+ unlock_page(page);
spd.pages[spd.nr_pages++] = page;
index++;
}
- /*
- * Now loop over the map and see if we need to start IO on any
- * pages, fill in the partial map, etc.
- */
index = *ppos >> PAGE_CACHE_SHIFT;
nr_pages = spd.nr_pages;
spd.nr_pages = 0;
+
for (page_nr = 0; page_nr < nr_pages; page_nr++) {
unsigned int this_len;
if (!len)
break;
- /*
- * this_len is the max we'll use from this page
- */
this_len = min_t(unsigned long, len, PAGE_CACHE_SIZE - loff);
page = spd.pages[page_nr];
- if (PageReadahead(page))
- page_cache_async_readahead(mapping, &in->f_ra, in,
- page, index, req_pages - page_nr);
-
- /*
- * If the page isn't uptodate, we may need to start io on it
- */
- if (!PageUptodate(page)) {
- lock_page(page);
-
- /*
- * Page was truncated, or invalidated by the
- * filesystem. Redo the find/create, but this time the
- * page is kept locked, so there's no chance of another
- * race with truncate/invalidate.
- */
- if (!page->mapping) {
- unlock_page(page);
- page = find_or_create_page(mapping, index,
- mapping_gfp_mask(mapping));
-
- if (!page) {
- error = -ENOMEM;
- break;
- }
- page_cache_release(spd.pages[page_nr]);
- spd.pages[page_nr] = page;
- }
- /*
- * page was already under io and is now done, great
- */
- if (PageUptodate(page)) {
- unlock_page(page);
- goto fill_it;
- }
-
- /*
- * need to read in the page
- */
- error = mapping->a_ops->readpage(in, page);
- if (unlikely(error)) {
- /*
- * We really should re-lookup the page here,
- * but it complicates things a lot. Instead
- * lets just do what we already stored, and
- * we'll get it the next time we are called.
- */
- if (error == AOP_TRUNCATED_PAGE)
- error = 0;
-
+ if (!PageUptodate(page) || page->mapping != mapping) {
+ page = NULL;
+ error = shmem_getpage(inode, index, &page,
+ SGP_CACHE, NULL);
+ if (error)
break;
- }
+ unlock_page(page);
+ page_cache_release(spd.pages[page_nr]);
+ spd.pages[page_nr] = page;
}
-fill_it:
- /*
- * i_size must be checked after PageUptodate.
- */
- isize = i_size_read(mapping->host);
+
+ isize = i_size_read(inode);
end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
if (unlikely(!isize || index > end_index))
break;
- /*
- * if this is the last page, see if we need to shrink
- * the length and stop
- */
if (end_index == index) {
unsigned int plen;
- /*
- * max good bytes in this page
- */
plen = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
if (plen <= loff)
break;
- /*
- * force quit after adding this page
- */
this_len = min(this_len, plen - loff);
len = this_len;
}
@@ -2040,13 +1945,8 @@ fill_it:
index++;
}
- /*
- * Release any pages at the end, if we quit early. 'page_nr' is how far
- * we got, 'nr_pages' is how many pages are in the map.
- */
while (page_nr < nr_pages)
page_cache_release(spd.pages[page_nr++]);
- in->f_ra.prev_pos = (loff_t)index << PAGE_CACHE_SHIFT;
if (spd.nr_pages)
error = splice_to_pipe(pipe, &spd);
--
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