On Wed, Sep 14, 2016 at 3:11 PM, Raslan, KarimAllah <karah...@amazon.de> wrote: > > Ahmed, Karim Allah > karah...@amazon.de > > > >> On Sep 15, 2016, at 12:05 AM, Dan Williams <dan.j.willi...@intel.com> wrote: >> >> On Wed, Sep 14, 2016 at 2:40 PM, Raslan, KarimAllah <karah...@amazon.de> >> wrote: >>> >>> >>> On 6/20/16, 10:23 AM, "Michal Hocko" <mho...@kernel.org> 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? > > I did expand the commit message in v2 of this patch to answer these questions: > > https://patchwork.kernel.org/patch/9190737/ >
Ah, ok that gives more information about how it is "potentially" problematic, so I assume you are hitting those problems in practice? That way the patch can be marked for -stable if this is a problem others are likely to run into in older kernels. When pfn_valid() fails does /proc/iomem show that address "System RAM"? If not then we could alternatively convert these problematic usages to use region_intersects().
