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@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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parent
708e3508c2
commit
71f0e07a60
128
mm/shmem.c
128
mm/shmem.c
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@ -1850,6 +1850,7 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
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unsigned int flags)
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{
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struct address_space *mapping = in->f_mapping;
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struct inode *inode = mapping->host;
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unsigned int loff, nr_pages, req_pages;
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struct page *pages[PIPE_DEF_BUFFERS];
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struct partial_page partial[PIPE_DEF_BUFFERS];
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@ -1865,7 +1866,7 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
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.spd_release = spd_release_page,
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};
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isize = i_size_read(in->f_mapping->host);
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isize = i_size_read(inode);
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if (unlikely(*ppos >= isize))
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return 0;
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@ -1881,153 +1882,57 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
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req_pages = (len + loff + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
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nr_pages = min(req_pages, pipe->buffers);
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/*
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* Lookup the (hopefully) full range of pages we need.
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*/
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spd.nr_pages = find_get_pages_contig(mapping, index,
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nr_pages, spd.pages);
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index += spd.nr_pages;
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/*
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* If find_get_pages_contig() returned fewer pages than we needed,
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* readahead/allocate the rest and fill in the holes.
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*/
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if (spd.nr_pages < nr_pages)
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page_cache_sync_readahead(mapping, &in->f_ra, in,
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index, req_pages - spd.nr_pages);
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error = 0;
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while (spd.nr_pages < nr_pages) {
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/*
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* Page could be there, find_get_pages_contig() breaks on
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* the first hole.
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*/
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page = find_get_page(mapping, index);
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if (!page) {
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/*
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* page didn't exist, allocate one.
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*/
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page = page_cache_alloc_cold(mapping);
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if (!page)
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page = NULL;
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error = shmem_getpage(inode, index, &page, SGP_CACHE, NULL);
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if (error)
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break;
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error = add_to_page_cache_lru(page, mapping, index,
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GFP_KERNEL);
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if (unlikely(error)) {
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page_cache_release(page);
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if (error == -EEXIST)
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continue;
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break;
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}
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/*
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* add_to_page_cache() locks the page, unlock it
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* to avoid convoluting the logic below even more.
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*/
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unlock_page(page);
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}
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spd.pages[spd.nr_pages++] = page;
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index++;
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}
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/*
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* Now loop over the map and see if we need to start IO on any
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* pages, fill in the partial map, etc.
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*/
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index = *ppos >> PAGE_CACHE_SHIFT;
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nr_pages = spd.nr_pages;
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spd.nr_pages = 0;
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for (page_nr = 0; page_nr < nr_pages; page_nr++) {
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unsigned int this_len;
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if (!len)
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break;
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/*
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* this_len is the max we'll use from this page
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*/
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this_len = min_t(unsigned long, len, PAGE_CACHE_SIZE - loff);
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page = spd.pages[page_nr];
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if (PageReadahead(page))
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page_cache_async_readahead(mapping, &in->f_ra, in,
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page, index, req_pages - page_nr);
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/*
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* If the page isn't uptodate, we may need to start io on it
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*/
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if (!PageUptodate(page)) {
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lock_page(page);
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/*
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* Page was truncated, or invalidated by the
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* filesystem. Redo the find/create, but this time the
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* page is kept locked, so there's no chance of another
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* race with truncate/invalidate.
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*/
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if (!page->mapping) {
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unlock_page(page);
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page = find_or_create_page(mapping, index,
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mapping_gfp_mask(mapping));
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if (!page) {
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error = -ENOMEM;
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if (!PageUptodate(page) || page->mapping != mapping) {
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page = NULL;
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error = shmem_getpage(inode, index, &page,
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SGP_CACHE, NULL);
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if (error)
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break;
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}
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unlock_page(page);
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page_cache_release(spd.pages[page_nr]);
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spd.pages[page_nr] = page;
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}
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/*
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* page was already under io and is now done, great
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*/
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if (PageUptodate(page)) {
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unlock_page(page);
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goto fill_it;
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}
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/*
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* need to read in the page
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*/
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error = mapping->a_ops->readpage(in, page);
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if (unlikely(error)) {
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/*
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* We really should re-lookup the page here,
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* but it complicates things a lot. Instead
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* lets just do what we already stored, and
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* we'll get it the next time we are called.
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*/
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if (error == AOP_TRUNCATED_PAGE)
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error = 0;
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break;
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}
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}
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fill_it:
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/*
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* i_size must be checked after PageUptodate.
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*/
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isize = i_size_read(mapping->host);
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isize = i_size_read(inode);
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end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
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if (unlikely(!isize || index > end_index))
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break;
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/*
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* if this is the last page, see if we need to shrink
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* the length and stop
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*/
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if (end_index == index) {
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unsigned int plen;
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/*
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* max good bytes in this page
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*/
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plen = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
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if (plen <= loff)
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break;
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/*
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* force quit after adding this page
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*/
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this_len = min(this_len, plen - loff);
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len = this_len;
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}
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@ -2040,13 +1945,8 @@ fill_it:
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index++;
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}
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/*
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* Release any pages at the end, if we quit early. 'page_nr' is how far
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* we got, 'nr_pages' is how many pages are in the map.
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*/
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while (page_nr < nr_pages)
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page_cache_release(spd.pages[page_nr++]);
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in->f_ra.prev_pos = (loff_t)index << PAGE_CACHE_SHIFT;
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if (spd.nr_pages)
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error = splice_to_pipe(pipe, &spd);
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