On 03/19/2018 08:11 PM, Olivier Matz wrote:
+ *
+ * if we don't need our mempools to have physically contiguous objects,
+ * then just set page shift and page size to 0, because the user has
+ * indicated that there's no need to care about anything.
+ *
+ * if we do need contiguous objects, there is also an option to reserve
+ * the entire mempool memory as one contiguous block of memory, in
+ * which case the page shift and alignment wouldn't matter as well.
+ *
+ * if we require contiguous objects, but not necessarily the entire
+ * mempool reserved space to be contiguous, then there are two options.
+ *
+ * if our IO addresses are virtual, not actual physical (IOVA as VA
+ * case), then no page shift needed - our memory allocation will give us
+ * contiguous physical memory as far as the hardware is concerned, so
+ * act as if we're getting contiguous memory.
+ *
+ * if our IO addresses are physical, we may get memory from bigger
+ * pages, or we might get memory from smaller pages, and how much of it
+ * we require depends on whether we want bigger or smaller pages.
+ * However, requesting each and every memory size is too much work, so
+ * what we'll do instead is walk through the page sizes available, pick
+ * the smallest one and set up page shift to match that one. We will be
+ * wasting some space this way, but it's much nicer than looping around
+ * trying to reserve each and every page size.
+ */
This comment is helpful to understand, thanks.
(by the way, reading it makes me think we should rename
MEMPOOL_F_*_PHYS_CONTIG as MEMPOOL_F_*_IOVA_CONTIG)
I'll care about renaming in my patchset about mempool_ops API.
