[PATCH v6 01/12] NFSD: Make the DRC size limit independent of page size

[Chuck Lever <cel@kernel.org>]

nfsd_cache_size_limit() takes the square root of the low-memory page
count and then shifts the result by the page size in KB. The shift
belongs under the root. A host with 64 KB pages has a page count 16
times smaller than a 4 KB host with the same memory, so its root is
4 times smaller and its shift 16 times larger, and the limit comes
out 4 times larger. With 8 GB of low memory the limit is 92672
entries on 4 KB pages and 370688 on 64 KB pages.

Take the root of the byte count instead. The result matches the
table above the function on every page size. Low memory on a 32-bit
host is under 1 GB, so the byte count fits in an unsigned long.

Fixes: 0338dd157282 ("nfsd: dynamically allocate DRC entries")
Suggested-by: NeilBrown <neil@brown.name>
Signed-off-by: Chuck Lever <cel@kernel.org>
---
 fs/nfsd/nfscache.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c
index 80364b91331a..b43b276a92b3 100644
--- a/fs/nfsd/nfscache.c
+++ b/fs/nfsd/nfscache.c
@@ -73,7 +73,7 @@ nfsd_cache_size_limit(void)
 	unsigned int limit;
 	unsigned long low_pages = totalram_pages() - totalhigh_pages();
 
-	limit = (16 * int_sqrt(low_pages)) << (PAGE_SHIFT-10);
+	limit = int_sqrt(low_pages << PAGE_SHIFT);
 	return min_t(unsigned int, limit, 256*1024);
 }
 

-- 
2.55.0