On Wed, May 25, 2022 at 10:59 AM Yang Shi <shy828301@xxxxxxxxx> wrote: > > On Tue, May 17, 2022 at 3:35 PM Zach O'Keefe <zokeefe@xxxxxxxxxx> wrote: > > > > On Tue, May 17, 2022 at 10:51 AM Yang Shi <shy828301@xxxxxxxxx> wrote: > > > > > > On Fri, May 13, 2022 at 4:56 PM Zach O'Keefe <zokeefe@xxxxxxxxxx> wrote: > > > > > > > > On Fri, May 13, 2022 at 4:17 PM Yang Shi <shy828301@xxxxxxxxx> wrote: > > > > > > > > > > On Fri, May 13, 2022 at 4:05 PM Zach O'Keefe <zokeefe@xxxxxxxxxx> wrote: > > > > > > > > > > > > Thanks for the review, David! > > > > > > > > > > > > On Thu, May 12, 2022 at 1:02 PM David Rientjes <rientjes@xxxxxxxxxx> wrote: > > > > > > > > > > > > > > On Wed, 4 May 2022, Zach O'Keefe wrote: > > > > > > > > > > > > > > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > > > > > > > index c94bc43dff3e..6095fcb3f07c 100644 > > > > > > > > --- a/mm/khugepaged.c > > > > > > > > +++ b/mm/khugepaged.c > > > > > > > > @@ -92,6 +92,10 @@ struct collapse_control { > > > > > > > > > > > > > > > > /* Last target selected in khugepaged_find_target_node() */ > > > > > > > > int last_target_node; > > > > > > > > + > > > > > > > > + struct page *hpage; > > > > > > > > + int (*alloc_charge_hpage)(struct mm_struct *mm, > > > > > > > > + struct collapse_control *cc); > > > > > > > > }; > > > > > > > > > > > > > > > > /** > > > > > > > > > > > > > > Embedding this function pointer into collapse_contol seems like it would > > > > > > > need some pretty strong rationale. Not to say that it should be a > > > > > > > non-starter, but I think the changelog needs to clearly indicate why this > > > > > > > is better/cleaner than embedding the needed info for a single allocation > > > > > > > and charge function to use. If the callbacks would truly be so different > > > > > > > that unifying them would be more complex, I think this makes sense. > > > > > > > > > > > > Mostly, this boils down to khugepaged having different a allocation > > > > > > pattern for NUMA/UMA ; the former scans the pages first to determine > > > > > > the right node, the latter preallocates before scanning. khugepaged > > > > > > has the luxury on UMA systems of just holding onto a hugepage > > > > > > indefinitely for the next collapse target. > > > > > > > > > > > > For MADV_COLLAPSE, we never preallocate, and so its pattern doesn't > > > > > > depend on NUMA or UMA configs. Trying to avoid "if (khugepaged) ... > > > > > > else" casing, defining this as a context-defined operation seemed > > > > > > appropriate. > > > > > > > > > > > > Collapsing both alloc and charging together was mostly a code > > > > > > cleanliness decision resulting from not wanting to embed a ->gfp() > > > > > > hook (gfp flags are used both by allocation and memcg charging). > > > > > > Alternatively, a .gfp member could exist - it would just need to be > > > > > > refreshed periodically in the khugepaged codepath. > > > > > > > > > > > > That all said - let me take another crack at seeing if I can make this > > > > > > work without the need for a function pointer here. > > > > > > > > > > I had a patch that removed UMA allocation, please refer to > > > > > https://lore.kernel.org/linux-mm/20210817202146.3218-1-shy828301@xxxxxxxxx/#t > > > > > > > > > > It was not made upstream due to some requests for further cleanup, but > > > > > unfortunately I haven't got time to look into it yet. > > > > > > > > > > If this page were merged, would that make your life easier? > > > > > > > > Hey Yang, > > > > > > > > First, sorry for missing that patch in the first place. I actually > > > > have some patches queued up that do a similar cleanup of > > > > khugepaged_prealloc_page() that was mentioned, but decided to not > > > > include them here. > > > > > > > > Second, removing the NUMA/UMA story does make this patch easier, I > > > > think (esp since the sched change was dropped for now). This is > > > > something I wanted while writing this series, but without the larger > > > > context referenced in your patch (most users don't build NUMA=n even > > > > on single node systems, and the pcp hugepage lists optimization) > > > > couldn't justify myself. > > > > > > Thanks, it would be better to add this patch into your series as a > > > prerequisite so that you could make the MADV_COLLAPSE easier. > > > > > > I don't think I will be able to find time to rework the patch and > > > solve all the review comments at any time soon. If you'd like to take > > > it, please do it. > > > > > > > Sounds good, Yang. I'll take a crack at it for v6. > > Hi Zach, > > Fortunately I got some time, if you haven't spent too much effort in > this, I could rework the patch then resubmit. Just let me know. > Hey Yang, Thanks for letting me know. In my v6 series, I actually ended up incorporating this work *afterwards*. Reason being there are some patches in my series, like "mm/khugepaged: pipe enum scan_result codes back to callers" which makes cleanup of khugepaged_scan_mm_slot() and khugepaged_scan_mm_slot() easier, IMO[1]. I'll privately send what I have planned for v6 and we can discuss. Thanks, Zach [1] https://lore.kernel.org/linux-mm/20220504214437.2850685-6-zokeefe@xxxxxxxxxx/ > > > > Thanks for taking the time, > > Zach > > > > > > > > > > Best, > > > > Zach