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Message-ID: <52162F4C.3090205@hp.com> Date: Thu, 22 Aug 2013 15:33:32 +0000 From: Thavatchai Makphaibulchoke <thavatchai.makpahibulchoke@...com> To: Linus Torvalds <torvalds@...ux-foundation.org> CC: T Makphaibulchoke <tmac@...com>, Theodore Ts'o <tytso@....edu>, "adilger.kernel@...ger.ca" <adilger.kernel@...ger.ca>, Al Viro <viro@...iv.linux.org.uk>, "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, "Chandramouleeswaran, Aswin" <aswin@...com> Subject: Re: [PATCH v2 1/2] mbcache: decoupling the locking of local from global data Thanks for the comments. On 08/22/2013 04:53 PM, Linus Torvalds wrote: > > Please don't do these ugly and pointless preprocessor macro expanders > that hide what the actual operation is. > > The DEBUG case seems to be just for your own testing anyway, so even > that shouldn't exist in the merged version. > Sorry, will clean them all up. > > And this is really ugly. Again it's also then hidden behind the ugly macro. > > First off, the thousand-time retry seems completely excessive. Does it > actually need any retry AT ALL? If the hash entry changes, either you > should retry forever, or if you feel that can result in livelocks > (fair enough) and you need a fallback case to a bigger lock, then why > not just do the fallback immediately? > > More importantly, regardless of that retry issue, this seems to be > abstracted at the wrong level, resulting in every single user of this > repeating the same complex and hard-to-understand incantation: > Looks like this is a misjudgement on my part. There is really no need to guard against mb_cache_entry from moving to a different hash chain, as the shrinking and allocation function already protecting against each other thorugh mb_cache_spinlock. The retry is not needed. > > where the only difference is that the last one doesn't unlock > afterwards because it runs in a loop with that LRU list lock held. > Ugh. Followed the above logic, all these pieces of code are also not necessary and could be just a simple unhash, as the original. > > The locking logic also isn't explained anywhere, making the > hard-to-read code even harder to read. Will add comment, explaining the locking logic. > > Linus > 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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