Hello,
I'd like to attend this year LSF/MM summit. Some topics of my interest
would be:
1) userfaultfd WP and soft-dirty interaction (i.e. obsolete
soft-dirty). Arch-dependent changes are required for this: from
one-more VM_FAULT_RETRY in a row to be returned by handle_mm_fault,
to a special bit in pagetable and swap entry, very similarly to
what soft dirty has been doing.
The main rationale to eventually obsolete soft-dirty is that
userfaultfd WP won't require O(N) pagetable scans to find out which
pages got dirty (where N is the number of pagetables mapping the
region to be monitored, not the number of pages that got
dirty). userfaultfd will have the same runtime cost regardless of
the size of the area to be monitored for writes, similar to PML
(Page Modification Logging) feature in the CPU for VMX.
soft-dirty is also triggering write protect faults, the only
advantage it has for some usage (which is a disadvantage for other
usages like database/KVM live snapshotting) is it's asynchronous,
but userfaultfs can also add an asynchronous feature mode later by
allocating and queuing up uffd messages, instead of blocking the
tasks.
If there's interested I could also summarize the current
userfaultfd status with hugetlbfs/shmem/non-cooperative support
currently merged in -mm.
2) the s/zone/node/ conversion of the page LRU feels still incomplete,
as compaction still works zone based and can't compact memory
crossing the zone boundaries. While it's is simpler to do
compaction that way, it's not ideal because reclaim works node
based.
To avoid dropping some patches that implement "compaction aware
zone_reclaim_mode" (i.e. now node_reclaim_mode) I'm still running
with zone LRU, although I don't disagree with the node LRU per se,
my only issue is that compaction still work zone based and that
collides with those changes.
With reclaim working node based and compaction working zone
based, I would need to call a blind for_each_zone(node)
compaction() loop which is far from ideal compared to compaction
crossing the zone boundary. Most pages that can be migrated by
compaction can go in any zone, not all but we could record the page
classzone.
On a side note just yesterday I got this message from kbuild bot:
---
FYI, we noticed a 7.2% improvement of pbzip2.throughput due to commit:
commit: 59ebc9c2dff1bd6476f621e1c9802dc40c8c5e98 ("Revert
"mm/page_alloc.c: recalculate some of node threshold when
on/offline memory"")
https://git.kernel.org/pub/scm/linux/kernel/git/andrea/aa.git master
---
This may be a statistical blip, I didn't investigate why zone LRU
should be faster for this test but I assume kbuild is reliable and
the result reproducible.
3) I'm always interested in the THP related developments, from native
swapout (perhaps native swapin) to ext4 support etc..
Thank you,
Andrea
--
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>
