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Message-ID: <5228A1AB.2030308@hp.com> Date: Thu, 05 Sep 2013 15:22:19 +0000 From: Thavatchai Makphaibulchoke <thavatchai.makpahibulchoke@...com> To: Andreas Dilger <adilger@...ger.ca> CC: T Makphaibulchoke <tmac@...com>, Theodore Ts'o <tytso@....edu>, Al Viro <viro@...iv.linux.org.uk>, "linux-ext4@...r.kernel.org List" <linux-ext4@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, "linux-fsdevel@...r.kernel.org Devel" <linux-fsdevel@...r.kernel.org>, aswin@...com, Linus Torvalds <torvalds@...ux-foundation.org>, aswin_proj@...ups.hp.com Subject: Re: [PATCH v3 0/2] ext4: increase mbcache scalability On 09/04/2013 08:00 PM, Andreas Dilger wrote: > > In the past, I've raised the question of whether mbcache is even > useful on real-world systems. Essentially, this is providing a > "deduplication" service for ext2/3/4 xattr blocks that are identical. > The question is how often this is actually the case in modern use? > The original design was for allowing external ACL blocks to be > shared between inodes, at a time when ACLs where pretty much the > only xattrs stored on inodes. > > The question now is whether there are common uses where all of the > xattrs stored on multiple inodes are identical? If that is not the > case, mbcache is just adding overhead and should just be disabled > entirely instead of just adding less overhead. > > There aren't good statistics on the hit rate for mbcache, but it > might be possible to generate some with systemtap or similar to > see how often ext4_xattr_cache_find() returns NULL vs. non-NULL. > > Cheers, Andreas > Looks like it's a bit harder to disable mbcache than I thought. I ended up adding code to collect the statics. With selinux enabled, for new_fserver workload of aim7, there are a total of 0x7e05420100000000 ext4_xattr_cache_find() calls that result in a hit and 0xc100000000000000 calls that are not. The number does not seem to favor the complete disabling of mbcache in this case. Thanks, Mak. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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