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Date: Mon, 07 Apr 2014 09:40:28 -0700 From: Andi Kleen <andi@...stfloor.org> To: Jan Kara <jack@...e.cz> Cc: Daniel J Blueman <daniel@...ascale.com>, Theodore Ts'o <tytso@....edu>, linux-ext4@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>, Steffen Persvold <sp@...ascale.com>, Andreas Dilger <adilger.kernel@...ger.ca> Subject: Re: ext4 performance falloff Jan Kara <jack@...e.cz> writes: > > What we really need is a counter where we can better estimate counts > accumulated in the percpu part of it. As the counter approaches zero, it's > CPU overhead will have to become that of a single locked variable but when > the value of counter is relatively high, we want it to be fast as the > percpu one. Possibly, each CPU could "reserve" part of the value in the > counter (by just decrementing the total value; how large that part should > be really needs to depend to the total value of the counter and number of > CPUs - in this regard we really differ from classical percpu couters) and > allocate/free using that part. If CPU cannot reserve what it is asked for > anymore, it would go and steal from parts other CPUs have accumulated, > returning them to global pool until it can satisfy the allocation. That's a percpu_counter() isn't it? (or cookie jar) The MM uses similar techniques. -Andi -- ak@...ux.intel.com -- Speaking for myself only -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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