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-rw-r--r--mm/readahead.c33
1 files changed, 24 insertions, 9 deletions
diff --git a/mm/readahead.c b/mm/readahead.c
index 9f0b98227b4..ba7db816f4c 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -53,13 +53,24 @@ static inline unsigned long get_min_readahead(struct file_ra_state *ra)
return (VM_MIN_READAHEAD * 1024) / PAGE_CACHE_SIZE;
}
+static inline void reset_ahead_window(struct file_ra_state *ra)
+{
+ /*
+ * ... but preserve ahead_start + ahead_size value,
+ * see 'recheck:' label in page_cache_readahead().
+ * Note: We never use ->ahead_size as rvalue without
+ * checking ->ahead_start != 0 first.
+ */
+ ra->ahead_size += ra->ahead_start;
+ ra->ahead_start = 0;
+}
+
static inline void ra_off(struct file_ra_state *ra)
{
ra->start = 0;
ra->flags = 0;
ra->size = 0;
- ra->ahead_start = 0;
- ra->ahead_size = 0;
+ reset_ahead_window(ra);
return;
}
@@ -73,10 +84,10 @@ static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
{
unsigned long newsize = roundup_pow_of_two(size);
- if (newsize <= max / 64)
- newsize = newsize * newsize;
+ if (newsize <= max / 32)
+ newsize = newsize * 4;
else if (newsize <= max / 4)
- newsize = max / 4;
+ newsize = newsize * 2;
else
newsize = max;
return newsize;
@@ -427,8 +438,7 @@ static int make_ahead_window(struct address_space *mapping, struct file *filp,
* congestion. The ahead window will any way be closed
* in case we failed due to excessive page cache hits.
*/
- ra->ahead_start = 0;
- ra->ahead_size = 0;
+ reset_ahead_window(ra);
}
return ret;
@@ -521,11 +531,11 @@ page_cache_readahead(struct address_space *mapping, struct file_ra_state *ra,
* If we get here we are doing sequential IO and this was not the first
* occurence (ie we have an existing window)
*/
-
if (ra->ahead_start == 0) { /* no ahead window yet */
if (!make_ahead_window(mapping, filp, ra, 0))
- goto out;
+ goto recheck;
}
+
/*
* Already have an ahead window, check if we crossed into it.
* If so, shift windows and issue a new ahead window.
@@ -537,11 +547,16 @@ page_cache_readahead(struct address_space *mapping, struct file_ra_state *ra,
ra->start = ra->ahead_start;
ra->size = ra->ahead_size;
make_ahead_window(mapping, filp, ra, 0);
+recheck:
+ /* prev_page shouldn't overrun the ahead window */
+ ra->prev_page = min(ra->prev_page,
+ ra->ahead_start + ra->ahead_size - 1);
}
out:
return ra->prev_page + 1;
}
+EXPORT_SYMBOL_GPL(page_cache_readahead);
/*
* handle_ra_miss() is called when it is known that a page which should have