> On Thu, Mar 25, 2010 at 11:47:17AM +0900, KOSAKI Motohiro wrote: > > > On Tue, Mar 23, 2010 at 09:22:04AM +0900, KOSAKI Motohiro wrote: > > > > > > > + /* > > > > > > > + * Index is between 0 and 1 so return within 3 decimal places > > > > > > > + * > > > > > > > + * 0 => allocation would fail due to lack of memory > > > > > > > + * 1 => allocation would fail due to fragmentation > > > > > > > + */ > > > > > > > + return 1000 - ( (1000+(info->free_pages * 1000 / requested)) / info->free_blocks_total); > > > > > > > +} > > > > > > > > > > > > Dumb question. > > > > > > your paper (http://portal.acm.org/citation.cfm?id=1375634.1375641) says > > > > > > fragmentation_index = 1 - (TotalFree/SizeRequested)/BlocksFree > > > > > > but your code have extra '1000+'. Why? > > > > > > > > > > To get an approximation to three decimal places. > > > > > > > > Do you mean this is poor man's round up logic? > > > > > > Not exactly. > > > > > > The intention is to have a value of 968 instead of 0.968231. i.e. > > > instead of a value between 0 and 1, it'll be a value between 0 and 1000 > > > that matches the first three digits after the decimal place. > > > > Let's consider extream case. > > > > free_pages: 1 > > requested: 1 > > free_blocks_total: 1 > > > > frag_index = 1000 - ((1000 + 1*1000/1))/1 = -1000 > > > > This is not your intension, I guess. > > Why not? > > See this comment > > /* Fragmentation index only makes sense when a request would fail */ > > In your example, there is a free page of the requested size so the allocation > would succeed. In this case, fragmentation index does indeed go negative > but the value is not useful. > > > Probably we don't need any round_up/round_down logic. because fragmentation_index > > is only used "if (fragindex >= 0 && fragindex <= 500)" check in try_to_compact_pages(). > > +1 or -1 inaccurate can be ignored. iow, I think we can remove '1000+' expression. > > > > This isn't about rounding, it's about having a value that normally is > between 0 and 1 expressed as a number between 0 and 1000 because we > can't use double in the kernel. Sorry, My example was wrong. new example is here. free_pages: 4 requested: 2 free_blocks_total: 4 theory: 1 - (TotalFree/SizeRequested)/BlocksFree = 1 - (4/2)/4 = 0.5 code : 1000 - ((1000 + 4*1000/2))/4 = 1000 - (1000 + 2000)/4 = 1000/4 = 250 I don't think this is three decimal picking up code. This seems might makes lots compaction invocation rather than theory. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>