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Subject[PATCH] better drop-behind in generic_file_write
Hi Linus, Daniel,

the (trivial) patch below fixes the drop-behind call in
generic_file_write to *only* do drop-behind if we've
written "past the end" of the page.

This way we have a better chance of still having partially
written pages in memory when we write to them again (eg. for
TUX logfiles). Not only will this speed up non page-aligned
writes on loaded systems, it'll also give slower writes a
small advantage over fast writes (which will skip page boundaries
more often).

Linus, Alan, could you please apply this patch in your next
2.4.0-test kernel ?

regards,

Rik
--
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Trailer at 11.

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--- linux-2.4.0-test12-pre3/mm/filemap.c.orig 2000/12/21 18:20:17
+++ linux/mm/filemap.c 2000/12/21 21:31:39
@@ -2436,7 +2436,7 @@
}

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

/*
@@ -2446,8 +2446,10 @@
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;
+ }

status = -ENOMEM; /* we'll assign it later anyway */
page = __grab_cache_page(mapping, index, &cached_page);
@@ -2478,9 +2480,17 @@
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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