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Message-ID: <20071016001850.GA19691@waste.org> Date: Mon, 15 Oct 2007 19:18:50 -0500 From: Matt Mackall <mpm@...enic.com> To: David Rientjes <rientjes@...gle.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org, Dave Hansen <haveblue@...ibm.com>, Rusty Russell <rusty@...tcorp.com.au>, Jeremy Fitzhardinge <jeremy@...p.org>, Fengguang Wu <wfg@...l.ustc.edu.cn> Subject: Re: [PATCH 1/11] maps3: add proportional set size accounting in smaps On Mon, Oct 15, 2007 at 04:36:38PM -0700, David Rientjes wrote: > On Mon, 15 Oct 2007, Matt Mackall wrote: > > > Index: l/fs/proc/task_mmu.c > > =================================================================== > > --- l.orig/fs/proc/task_mmu.c 2007-10-14 13:35:31.000000000 -0500 > > +++ l/fs/proc/task_mmu.c 2007-10-14 13:36:56.000000000 -0500 > > @@ -122,6 +122,27 @@ struct mem_size_stats > > unsigned long private_clean; > > unsigned long private_dirty; > > unsigned long referenced; > > + > > + /* > > + * Proportional Set Size(PSS): my share of RSS. > > + * > > + * PSS of a process is the count of pages it has in memory, where each > > + * page is divided by the number of processes sharing it. So if a > > + * process has 1000 pages all to itself, and 1000 shared with one other > > + * process, its PSS will be 1500. - Matt Mackall, lwn.net > > + */ > > + u64 pss; > > + /* > > + * To keep (accumulated) division errors low, we adopt 64bit pss and > > + * use some low bits for division errors. So (pss >> PSS_DIV_BITS) > > + * would be the real byte count. > > + * > > + * A shift of 12 before division means(assuming 4K page size): > > + * - 1M 3-user-pages add up to 8KB errors; > > + * - supports mapcount up to 2^24, or 16M; > > + * - supports PSS up to 2^52 bytes, or 4PB. > > + */ > > +#define PSS_DIV_BITS 12 > > }; > > > > I know this gets moved again in the eighth patch of the series, but the > #define still has no place inside the struct definition. Agreed. > The pss is going to need accessor functions, preferably inlined, and the > comment adjusted stating that all accesses should be through those > functions and not directly to the mem_size_stats struct. > > static inline u64 pss_up(unsigned long pss) > { > return pss << PSS_DIV_BITS; > } > > static inline unsigned long pss_down(u64 pss) > { > return pss >> PSS_DIV_BITS; > } I think that's overkill for something that has exactly one use of each. -- Mathematics is the supreme nostalgia of our time. - 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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