linux-kernel - [PATCH] Sanely size hash tables when using large base pages. take 2.

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Message-ID: <20070102210322.GA20697@linux-sh.org>
Date:	Wed, 3 Jan 2007 06:03:22 +0900
From:	Paul Mundt <lethal@...ux-sh.org>
To:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH] Sanely size hash tables when using large base pages. take 2.

This is a resubmission of the earlier patch with the pidhash bits
dropped.

At the moment the inode/dentry cache hash tables (common by way of
alloc_large_system_hash()) are incorrectly sized by their respective
detection logic when we attempt to use large base pages on systems
with little memory.

This results in odd behaviour when using a 64kB PAGE_SIZE, such as:

Dentry cache hash table entries: 8192 (order: -1, 32768 bytes)
Inode-cache hash table entries: 4096 (order: -2, 16384 bytes)

The mount cache hash table is seemingly the only one that gets this right
by directly taking PAGE_SIZE in to account.

The following patch attempts to catch the bogus values and round it up to
at least 0-order.

Signed-off-by: Paul Mundt <lethal@...ux-sh.org>

--

 mm/page_alloc.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8c1a116..4a9a83f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3321,6 +3321,10 @@ void *__init alloc_large_system_hash(con
 			numentries >>= (scale - PAGE_SHIFT);
 		else
 			numentries <<= (PAGE_SHIFT - scale);
+
+		/* Make sure we've got at least a 0-order allocation.. */
+		if (unlikely((numentries * bucketsize) < PAGE_SIZE))
+			numentries = PAGE_SIZE / bucketsize;
 	}
 	numentries = roundup_pow_of_two(numentries);

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