readahead: split ondemand readahead interface into two functions
Split ondemand readahead interface into two functions. I think this makes it a little clearer for non-readahead experts (like Rusty). Internally they both call ondemand_readahead(), but the page argument is changed to an obvious boolean flag. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Коммит
cf914a7d65
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@ -139,10 +139,10 @@ static int ext3_readdir(struct file * filp,
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pgoff_t index = map_bh.b_blocknr >>
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(PAGE_CACHE_SHIFT - inode->i_blkbits);
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if (!ra_has_index(&filp->f_ra, index))
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page_cache_readahead_ondemand(
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page_cache_sync_readahead(
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sb->s_bdev->bd_inode->i_mapping,
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&filp->f_ra, filp,
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NULL, index, 1);
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index, 1);
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filp->f_ra.prev_index = index;
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bh = ext3_bread(NULL, inode, blk, 0, &err);
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}
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@ -138,10 +138,10 @@ static int ext4_readdir(struct file * filp,
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pgoff_t index = map_bh.b_blocknr >>
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(PAGE_CACHE_SHIFT - inode->i_blkbits);
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if (!ra_has_index(&filp->f_ra, index))
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page_cache_readahead_ondemand(
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page_cache_sync_readahead(
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sb->s_bdev->bd_inode->i_mapping,
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&filp->f_ra, filp,
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NULL, index, 1);
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index, 1);
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filp->f_ra.prev_index = index;
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bh = ext4_bread(NULL, inode, blk, 0, &err);
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}
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@ -295,8 +295,8 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
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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_readahead_ondemand(mapping, &in->f_ra, in,
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NULL, index, req_pages - spd.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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@ -352,7 +352,7 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
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page = pages[page_nr];
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if (PageReadahead(page))
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page_cache_readahead_ondemand(mapping, &in->f_ra, in,
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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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@ -1138,12 +1138,20 @@ int do_page_cache_readahead(struct address_space *mapping, struct file *filp,
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pgoff_t offset, unsigned long nr_to_read);
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int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
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pgoff_t offset, unsigned long nr_to_read);
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unsigned long page_cache_readahead_ondemand(struct address_space *mapping,
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struct file_ra_state *ra,
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struct file *filp,
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struct page *page,
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pgoff_t offset,
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unsigned long size);
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void page_cache_sync_readahead(struct address_space *mapping,
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struct file_ra_state *ra,
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struct file *filp,
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pgoff_t offset,
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unsigned long size);
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void page_cache_async_readahead(struct address_space *mapping,
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struct file_ra_state *ra,
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struct file *filp,
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struct page *pg,
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pgoff_t offset,
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unsigned long size);
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unsigned long max_sane_readahead(unsigned long nr);
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/* Do stack extension */
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10
mm/filemap.c
10
mm/filemap.c
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@ -894,15 +894,15 @@ void do_generic_mapping_read(struct address_space *mapping,
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find_page:
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page = find_get_page(mapping, index);
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if (!page) {
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page_cache_readahead_ondemand(mapping,
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&ra, filp, page,
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page_cache_sync_readahead(mapping,
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&ra, filp,
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index, last_index - index);
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page = find_get_page(mapping, index);
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if (unlikely(page == NULL))
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goto no_cached_page;
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}
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if (PageReadahead(page)) {
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page_cache_readahead_ondemand(mapping,
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page_cache_async_readahead(mapping,
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&ra, filp, page,
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index, last_index - index);
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}
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@ -1348,14 +1348,14 @@ retry_find:
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*/
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if (VM_SequentialReadHint(vma)) {
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if (!page) {
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page_cache_readahead_ondemand(mapping, ra, file, page,
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page_cache_sync_readahead(mapping, ra, file,
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vmf->pgoff, 1);
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page = find_lock_page(mapping, vmf->pgoff);
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if (!page)
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goto no_cached_page;
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}
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if (PageReadahead(page)) {
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page_cache_readahead_ondemand(mapping, ra, file, page,
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page_cache_async_readahead(mapping, ra, file, page,
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vmf->pgoff, 1);
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}
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}
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@ -359,7 +359,7 @@ static unsigned long get_next_ra_size(struct file_ra_state *ra,
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static unsigned long
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ondemand_readahead(struct address_space *mapping,
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struct file_ra_state *ra, struct file *filp,
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struct page *page, pgoff_t offset,
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bool hit_readahead_marker, pgoff_t offset,
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unsigned long req_size)
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{
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unsigned long max; /* max readahead pages */
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@ -387,7 +387,7 @@ ondemand_readahead(struct address_space *mapping,
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* Standalone, small read.
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* Read as is, and do not pollute the readahead state.
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*/
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if (!page && !sequential) {
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if (!hit_readahead_marker && !sequential) {
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return __do_page_cache_readahead(mapping, filp,
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offset, req_size, 0);
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}
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@ -408,7 +408,7 @@ ondemand_readahead(struct address_space *mapping,
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* E.g. interleaved reads.
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* Not knowing its readahead pos/size, bet on the minimal possible one.
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*/
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if (page) {
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if (hit_readahead_marker) {
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ra_index++;
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ra_size = min(4 * ra_size, max);
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}
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@ -421,50 +421,71 @@ fill_ra:
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}
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/**
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* page_cache_readahead_ondemand - generic file readahead
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* page_cache_sync_readahead - generic file readahead
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* @mapping: address_space which holds the pagecache and I/O vectors
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* @ra: file_ra_state which holds the readahead state
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* @filp: passed on to ->readpage() and ->readpages()
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* @page: the page at @offset, or NULL if non-present
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* @offset: start offset into @mapping, in PAGE_CACHE_SIZE units
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* @offset: start offset into @mapping, in pagecache page-sized units
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* @req_size: hint: total size of the read which the caller is performing in
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* PAGE_CACHE_SIZE units
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* pagecache pages
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*
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* page_cache_readahead_ondemand() is the entry point of readahead logic.
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* This function should be called when it is time to perform readahead:
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* 1) @page == NULL
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* A cache miss happened, time for synchronous readahead.
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* 2) @page != NULL && PageReadahead(@page)
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* A look-ahead hit occured, time for asynchronous readahead.
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* page_cache_sync_readahead() should be called when a cache miss happened:
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* it will submit the read. The readahead logic may decide to piggyback more
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* pages onto the read request if access patterns suggest it will improve
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* performance.
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*/
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unsigned long
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page_cache_readahead_ondemand(struct address_space *mapping,
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struct file_ra_state *ra, struct file *filp,
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struct page *page, pgoff_t offset,
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unsigned long req_size)
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void page_cache_sync_readahead(struct address_space *mapping,
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struct file_ra_state *ra, struct file *filp,
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pgoff_t offset, unsigned long req_size)
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{
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/* no read-ahead */
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if (!ra->ra_pages)
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return 0;
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if (page) {
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/*
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* It can be PG_reclaim.
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*/
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if (PageWriteback(page))
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return 0;
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ClearPageReadahead(page);
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/*
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* Defer asynchronous read-ahead on IO congestion.
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*/
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if (bdi_read_congested(mapping->backing_dev_info))
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return 0;
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}
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return;
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/* do read-ahead */
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return ondemand_readahead(mapping, ra, filp, page,
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offset, req_size);
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ondemand_readahead(mapping, ra, filp, false, offset, req_size);
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}
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EXPORT_SYMBOL_GPL(page_cache_readahead_ondemand);
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EXPORT_SYMBOL_GPL(page_cache_sync_readahead);
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/**
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* page_cache_async_readahead - file readahead for marked pages
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* @mapping: address_space which holds the pagecache and I/O vectors
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* @ra: file_ra_state which holds the readahead state
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* @filp: passed on to ->readpage() and ->readpages()
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* @page: the page at @offset which has the PG_readahead flag set
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* @offset: start offset into @mapping, in pagecache page-sized units
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* @req_size: hint: total size of the read which the caller is performing in
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* pagecache pages
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*
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* page_cache_async_ondemand() should be called when a page is used which
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* has the PG_readahead flag: this is a marker to suggest that the application
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* has used up enough of the readahead window that we should start pulling in
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* more pages. */
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void
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page_cache_async_readahead(struct address_space *mapping,
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struct file_ra_state *ra, struct file *filp,
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struct page *page, pgoff_t offset,
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unsigned long req_size)
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{
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/* no read-ahead */
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if (!ra->ra_pages)
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return;
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/*
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* Same bit is used for PG_readahead and PG_reclaim.
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*/
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if (PageWriteback(page))
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return;
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ClearPageReadahead(page);
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/*
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* Defer asynchronous read-ahead on IO congestion.
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*/
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if (bdi_read_congested(mapping->backing_dev_info))
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return;
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/* do read-ahead */
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ondemand_readahead(mapping, ra, filp, true, offset, req_size);
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}
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EXPORT_SYMBOL_GPL(page_cache_async_readahead);
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