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Subject[PATCH] drop-behind fix for generic_file_write
Hi Linus, Alan,

the following (trivial) patch fixes drop-behind behaviour
in generic_file_write to only drop fully written pages.

This increases performance in dbench by about 8% (as
measured by Daniel Phillips) and should get rid of the
logfile bottleneck Ingo Molnar found with the drop-behind
call in generic_file_write in TUX tests.

Please apply this (trivial) patch for 2.4.0.

regards,

Rik
--
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Trailer at 11.

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--- linux-2.4.0-prerelease/mm/filemap.c.orig Wed Jan 3 12:52:13 2001
+++ linux-2.4.0-prerelease/mm/filemap.c Wed Jan 3 12:54:05 2001
@@ -2496,7 +2496,7 @@
}

while (count) {
- unsigned long bytes, index, offset;
+ unsigned long bytes, index, offset, partial = 0;
char *kaddr;

/*
@@ -2506,8 +2506,10 @@
offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */
index = pos >> PAGE_CACHE_SHIFT;
bytes = PAGE_CACHE_SIZE - offset;
- if (bytes > count)
+ if (bytes > count) {
bytes = count;
+ partial = 1;
+ }

/*
* Bring in the user page that we will copy from _first_.
@@ -2549,9 +2551,17 @@
buf += status;
}
unlock:
- /* Mark it unlocked again and drop the page.. */
+ /*
+ * Mark it unlocked again and release the page.
+ * In order to prevent large (fast) file writes
+ * from causing too much memory pressure we move
+ * completely written pages to the inactive list.
+ * We do, however, try to keep the pages that may
+ * still be written to (ie. partially written pages).
+ */
UnlockPage(page);
- deactivate_page(page);
+ if (!partial)
+ deactivate_page(page);
page_cache_release(page);

if (status < 0)
-
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