The patch titled
readahead: call scheme
has been added to the -mm tree. Its filename is
readahead-call-scheme.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: readahead: call scheme
From: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
The read-ahead logic is called when the reading hits
- a PG_readahead marked page;
- a non-present page.
ra.prev_page should be properly setup on entrance, and readahead_cache_hit()
should be called on every page reference as a feedback.
This call scheme achieves the following goals:
- makes all stateful/stateless methods happy;
- eliminates the cache hit problem naturally;
- lives in harmony with application managed read-aheads via
fadvise/madvise.
[efault@xxxxxx: fix leak encountered with rpm -qaV]
Signed-off-by: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
Signed-off-by: Mike Galbraith <efault@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
include/linux/mm.h | 16 ++++
mm/filemap.c | 42 +++++++++++-
mm/readahead.c | 143 +++++++++++++++++++++++++++++++++++++++++++
3 files changed, 197 insertions(+), 4 deletions(-)
diff -puN include/linux/mm.h~readahead-call-scheme include/linux/mm.h
--- a/include/linux/mm.h~readahead-call-scheme
+++ a/include/linux/mm.h
@@ -1067,6 +1067,22 @@ unsigned long page_cache_readahead(struc
void handle_ra_miss(struct address_space *mapping,
struct file_ra_state *ra, pgoff_t offset);
unsigned long max_sane_readahead(unsigned long nr);
+unsigned long
+page_cache_readahead_adaptive(struct address_space *mapping,
+ struct file_ra_state *ra,
+ struct file *filp,
+ struct page *page,
+ pgoff_t offset,
+ unsigned long size);
+
+#if defined(CONFIG_DEBUG_READAHEAD)
+void readahead_cache_hit(struct file_ra_state *ra, struct page *page);
+#else
+static inline void readahead_cache_hit(struct file_ra_state *ra,
+ struct page *page)
+{
+}
+#endif
#ifdef CONFIG_ADAPTIVE_READAHEAD
extern int readahead_ratio;
diff -puN mm/filemap.c~readahead-call-scheme mm/filemap.c
--- a/mm/filemap.c~readahead-call-scheme
+++ a/mm/filemap.c
@@ -945,16 +945,33 @@ void do_generic_mapping_read(struct addr
nr = nr - offset;
cond_resched();
- if (index == next_index)
+
+ if (!prefer_adaptive_readahead() && index == next_index)
next_index = page_cache_readahead(mapping, &ra, filp,
index, last_index - index);
find_page:
page = find_get_page(mapping, index);
+ if (prefer_adaptive_readahead()) {
+ if (unlikely(page == NULL)) {
+ ra.prev_page = prev_index;
+ page_cache_readahead_adaptive(mapping,
+ &ra, filp, NULL,
+ index, last_index - index);
+ page = find_get_page(mapping, index);
+ } else if (PageReadahead(page)) {
+ ra.prev_page = prev_index;
+ page_cache_readahead_adaptive(mapping,
+ &ra, filp, page,
+ index, last_index - index);
+ }
+ }
if (unlikely(page == NULL)) {
- handle_ra_miss(mapping, &ra, index);
+ if (!prefer_adaptive_readahead())
+ handle_ra_miss(mapping, &ra, index);
goto no_cached_page;
}
+ readahead_cache_hit(&ra, page);
if (!PageUptodate(page))
goto page_not_up_to_date;
page_ok:
@@ -1102,6 +1119,8 @@ no_cached_page:
out:
*_ra = ra;
+ if (prefer_adaptive_readahead())
+ _ra->prev_page = prev_index;
*ppos = ((loff_t) index << PAGE_CACHE_SHIFT) + offset;
if (cached_page)
@@ -1372,6 +1391,7 @@ struct page *filemap_nopage(struct vm_ar
unsigned long size, pgoff;
int did_readaround = 0, majmin = VM_FAULT_MINOR;
+ ra->flags |= RA_FLAG_MMAP;
pgoff = ((address-area->vm_start) >> PAGE_CACHE_SHIFT) + area->vm_pgoff;
retry_all:
@@ -1389,7 +1409,7 @@ retry_all:
*
* For sequential accesses, we use the generic readahead logic.
*/
- if (VM_SequentialReadHint(area))
+ if (!prefer_adaptive_readahead() && VM_SequentialReadHint(area))
page_cache_readahead(mapping, ra, file, pgoff, 1);
/*
@@ -1397,11 +1417,22 @@ retry_all:
*/
retry_find:
page = find_get_page(mapping, pgoff);
+ if (prefer_adaptive_readahead() && VM_SequentialReadHint(area)) {
+ if (!page) {
+ page_cache_readahead_adaptive(mapping, ra, file, NULL,
+ pgoff, 1);
+ page = find_get_page(mapping, pgoff);
+ } else if (PageReadahead(page)) {
+ page_cache_readahead_adaptive(mapping, ra, file, page,
+ pgoff, 1);
+ }
+ }
if (!page) {
unsigned long ra_pages;
if (VM_SequentialReadHint(area)) {
- handle_ra_miss(mapping, ra, pgoff);
+ if (!prefer_adaptive_readahead())
+ handle_ra_miss(mapping, ra, pgoff);
goto no_cached_page;
}
ra->mmap_miss++;
@@ -1437,6 +1468,7 @@ retry_find:
if (!did_readaround)
ra->mmap_hit++;
+ readahead_cache_hit(ra, page);
/*
* Ok, found a page in the page cache, now we need to check
@@ -1452,6 +1484,8 @@ success:
mark_page_accessed(page);
if (type)
*type = majmin;
+ if (prefer_adaptive_readahead())
+ ra->prev_page = page->index;
return page;
outside_data_content:
diff -puN mm/readahead.c~readahead-call-scheme mm/readahead.c
--- a/mm/readahead.c~readahead-call-scheme
+++ a/mm/readahead.c
@@ -1556,6 +1556,149 @@ static inline void get_readahead_bounds(
#endif /* CONFIG_ADAPTIVE_READAHEAD */
+/**
+ * page_cache_readahead_adaptive - thrashing safe adaptive read-ahead
+ * @mapping, @ra, @filp, @offset, @req_size: the same as page_cache_readahead()
+ * @page: the page at @offset, or NULL if non-present
+ *
+ * page_cache_readahead_adaptive() is the entry point of the adaptive
+ * read-ahead logic. It tries a set of methods in turn to determine the
+ * appropriate readahead action and submits the readahead I/O.
+ *
+ * This function is expected to be called on two conditions:
+ * 1. @page == NULL
+ * A cache miss happened, some pages have to be read in
+ * 2. @page != NULL && PageReadahead(@page)
+ * A look-ahead mark encountered, this is set by a previous read-ahead
+ * invocation to instruct the caller to give the function a chance to
+ * check up and do next read-ahead in advance.
+ */
+unsigned long
+page_cache_readahead_adaptive(struct address_space *mapping,
+ struct file_ra_state *ra, struct file *filp,
+ struct page *page,
+ pgoff_t offset, unsigned long req_size)
+{
+ unsigned long ra_size;
+ unsigned long ra_min;
+ unsigned long ra_max;
+ int ret;
+
+ if (page) {
+ ClearPageReadahead(page);
+
+ /*
+ * Defer read-ahead on IO congestion.
+ */
+ if (bdi_read_congested(mapping->backing_dev_info)) {
+ ra_account(ra, RA_EVENT_IO_CONGESTION, req_size);
+ return 0;
+ }
+ }
+
+ if (page)
+ ra_account(ra, RA_EVENT_LOOKAHEAD_HIT, ra_lookahead_size(ra));
+ else if (offset)
+ ra_account(ra, RA_EVENT_CACHE_MISS, req_size);
+
+ get_readahead_bounds(ra, &ra_min, &ra_max);
+
+ /* read-ahead disabled? */
+ if (unlikely(!ra_max || !readahead_ratio)) {
+ ra_size = max_sane_readahead(req_size);
+ goto readit;
+ }
+
+ /*
+ * Start of file.
+ */
+ if (offset == 0)
+ return initial_readahead(mapping, filp, ra, req_size);
+
+ /*
+ * State based sequential read-ahead.
+ */
+ if (offset == ra->prev_page + 1 &&
+ offset == ra->lookahead_index &&
+ !debug_option(disable_stateful_method))
+ return state_based_readahead(mapping, filp, ra, page,
+ offset, req_size, ra_max);
+
+ /*
+ * Recover from possible thrashing.
+ */
+ if (!page && offset == ra->prev_page + 1 && ra_has_index(ra, offset))
+ return thrashing_recovery_readahead(mapping, filp, ra,
+ offset, ra_max);
+
+ /*
+ * Backward read-ahead.
+ */
+ if (!page && try_backward_prefetching(ra, offset, req_size, ra_max))
+ return ra_submit(ra, mapping, filp);
+
+ /*
+ * Context based sequential read-ahead.
+ */
+ ret = try_context_based_readahead(mapping, ra, page,
+ offset, ra_min, ra_max);
+ if (ret > 0)
+ return ra_submit(ra, mapping, filp);
+ if (ret < 0)
+ return 0;
+
+ /* No action on look-ahead time? */
+ if (page) {
+ ra_account(ra, RA_EVENT_LOOKAHEAD_NOACTION,
+ ra->readahead_index - offset);
+ return 0;
+ }
+
+ /*
+ * Random read.
+ */
+ ra_size = min(req_size, ra_max);
+readit:
+ ra_size = __do_page_cache_readahead(mapping, filp, offset, ra_size, 0);
+
+ ra_account(ra, RA_EVENT_RANDOM_READ, ra_size);
+ dprintk("random_read(ino=%lu, req=%lu+%lu) = %lu\n",
+ mapping->host->i_ino, offset, req_size, ra_size);
+
+ return ra_size;
+}
+EXPORT_SYMBOL_GPL(page_cache_readahead_adaptive);
+
+#if CONFIG_DEBUG_READAHEAD
+/**
+ * readahead_cache_hit - adaptive read-ahead feedback function
+ * @ra: file_ra_state which holds the readahead state
+ * @page: the page just accessed
+ *
+ * This is the optional feedback route of the adaptive read-ahead logic.
+ * It must be called on every access on the read-ahead pages.
+ */
+void readahead_cache_hit(struct file_ra_state *ra, struct page *page)
+{
+ if (!prefer_adaptive_readahead())
+ return;
+
+ if (PageActive(page) || PageReferenced(page))
+ return;
+
+ if (!PageUptodate(page))
+ ra_account(ra, RA_EVENT_IO_BLOCK, 1);
+
+ if (!ra_has_index(ra, page->index))
+ return;
+
+ if (page->index >= ra->ra_index)
+ ra_account(ra, RA_EVENT_READAHEAD_HIT, 1);
+ else
+ ra_account(ra, RA_EVENT_READAHEAD_HIT, -1);
+}
+#endif /* CONFIG_DEBUG_READAHEAD */
+
/*
* Read-ahead events accounting.
*/
_
Patches currently in -mm which might be from wfg@xxxxxxxxxxxxxxxx are
readahead-kconfig-options.patch
radixtree-introduce-scan-hole-data-functions.patch
mm-introduce-probe_page.patch
mm-introduce-pg_readahead.patch
readahead-add-look-ahead-support-to-__do_page_cache_readahead.patch
readahead-insert-cond_resched-calls.patch
readahead-minmax_ra_pages.patch
readahead-events-accounting.patch
readahead-rescue_pages.patch
readahead-sysctl-parameters.patch
readahead-min-max-sizes.patch
readahead-state-based-method-aging-accounting.patch
readahead-state-based-method-routines.patch
readahead-state-based-method.patch
readahead-context-based-method.patch
readahead-initial-method-guiding-sizes.patch
readahead-initial-method-thrashing-guard-size.patch
readahead-initial-method-user-recommended-size.patch
readahead-initial-method.patch
readahead-backward-prefetching-method.patch
readahead-thrashing-recovery-method.patch
readahead-call-scheme.patch
readahead-laptop-mode.patch
readahead-loop-case.patch
readahead-nfsd-case.patch
readahead-turn-on-by-default.patch
readahead-remove-size-limit-on-read_ahead_kb.patch
readahead-remove-size-limit-of-max_sectors_kb-on-read_ahead_kb.patch
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