readahead: combine file_ra_state.prev_index/prev_offset into prev_pos
Combine the file_ra_state members
unsigned long prev_index
unsigned int prev_offset
into
loff_t prev_pos
It is more consistent and better supports huge files.
Thanks to Peter for the nice proposal!
[akpm@linux-foundation.org: fix shift overflow]
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/readahead.c b/mm/readahead.c
index d250487..4a58bef 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -46,7 +46,7 @@
file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping)
{
ra->ra_pages = mapping->backing_dev_info->ra_pages;
- ra->prev_index = -1;
+ ra->prev_pos = -1;
}
EXPORT_SYMBOL_GPL(file_ra_state_init);
@@ -327,7 +327,7 @@
* indicator. The flag won't be set on already cached pages, to avoid the
* readahead-for-nothing fuss, saving pointless page cache lookups.
*
- * prev_index tracks the last visited page in the _previous_ read request.
+ * prev_pos tracks the last visited byte in the _previous_ read request.
* It should be maintained by the caller, and will be used for detecting
* small random reads. Note that the readahead algorithm checks loosely
* for sequential patterns. Hence interleaved reads might be served as
@@ -351,11 +351,9 @@
bool hit_readahead_marker, pgoff_t offset,
unsigned long req_size)
{
- int max; /* max readahead pages */
- int sequential;
-
- max = ra->ra_pages;
- sequential = (offset - ra->prev_index <= 1UL) || (req_size > max);
+ int max = ra->ra_pages; /* max readahead pages */
+ pgoff_t prev_offset;
+ int sequential;
/*
* It's the expected callback offset, assume sequential access.
@@ -369,6 +367,9 @@
goto readit;
}
+ prev_offset = ra->prev_pos >> PAGE_CACHE_SHIFT;
+ sequential = offset - prev_offset <= 1UL || req_size > max;
+
/*
* Standalone, small read.
* Read as is, and do not pollute the readahead state.