On Wed, Sep 14, 2016 at 2:40 PM, Raslan, KarimAllah <karahmed@xxxxxxxxx> wrote: > > > On 6/20/16, 10:23 AM, "Michal Hocko" <mhocko@xxxxxxxxxx> wrote: > > On Sat 18-06-16 12:11:19, KarimAllah Ahmed wrote: > > When sparse memory model is used an array of memory sections is created to > > track each block of contiguous physical pages. Each element of this array > > contains PAGES_PER_SECTION pages. During the creation of this array the actual > > boundaries of the memory block is lost, so the whole block is either considered > > as present or not. > > > > pfn_valid() in the sparse memory configuration checks which memory sections the > > pfn belongs to then checks whether it's present or not. This yields sub-optimal > > results when the available memory doesn't cover the whole memory section, > > because pfn_valid will return 'true' even for the unavailable pfns at the > > boundaries of the memory section. > > Please be more verbose of _why_ the patch is needed. Why those > "sub-optimal results" matter? > > Does this make sense to you ? [ channeling my inner akpm ] What's the user visible effect of this change? What code is getting tripped up by pfn_valid() being imprecise, and why is changing pfn_valid() the preferred fix? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>