Re: [PATCH 0/8] make hugetlb put_page safe for all calling contexts

[Miaohe Lin]

Hi:
On 2021/3/25 8:28, Mike Kravetz wrote:
> This effort is the result a recent bug report [1].  In subsequent
> discussions [2], it was deemed necessary to properly fix the hugetlb

Many thanks for the effort. I have read the discussions and it is pretty long.
Maybe it would be helpful if you give a brief summary here?

> put_page path (free_huge_page).  This RFC provides a possible way to

trival: Not RFC here.

> address the issue.  Comments are welcome/encouraged as several attempts
> at this have been made in the past.
> > This series is based on v5.12-rc3-mmotm-2021-03-17-22-24.  At a high
> level, the series provides:
> - Patches 1 & 2 from Roman Gushchin provide cma_release_nowait()

trival: missing description of the Patches 3 ?

> - Patches 4, 5 & 6 are aimed at reducing lock hold times.  To be clear
>   the goal is to eliminate single lock hold times of a long duration.
>   Overall lock hold time is not addressed.
> - Patch 7 makes hugetlb_lock and subpool lock IRQ safe.  It also reverts
>   the code which defers calls to a workqueue if !in_task.
> - Patch 8 adds some lockdep_assert_held() calls
> 
> [1] https://lore.kernel.org/linux-mm/000000000000f1c03b05bc43aadc@xxxxxxxxxx/
> [2] http://lkml.kernel.org/r/20210311021321.127500-1-mike.kravetz@xxxxxxxxxx
> 
> RFC -> v1
> - Add Roman's cma_release_nowait() patches.  This eliminated the need
>   to do a workqueue handoff in hugetlb code.
> - Use Michal's suggestion to batch pages for freeing.  This eliminated
>   the need to recalculate loop control variables when dropping the lock.
> - Added lockdep_assert_held() calls
> - Rebased to v5.12-rc3-mmotm-2021-03-17-22-24
> 
> Mike Kravetz (6):
>   hugetlb: add per-hstate mutex to synchronize user adjustments
>   hugetlb: create remove_hugetlb_page() to separate functionality
>   hugetlb: call update_and_free_page without hugetlb_lock
>   hugetlb: change free_pool_huge_page to remove_pool_huge_page
>   hugetlb: make free_huge_page irq safe
>   hugetlb: add lockdep_assert_held() calls for hugetlb_lock
> 
> Roman Gushchin (2):
>   mm: cma: introduce cma_release_nowait()
>   mm: hugetlb: don't drop hugetlb_lock around cma_release() call
> 
>  include/linux/cma.h     |   2 +
>  include/linux/hugetlb.h |   1 +
>  mm/cma.c                |  93 +++++++++++
>  mm/cma.h                |   5 +
>  mm/hugetlb.c            | 354 +++++++++++++++++++++-------------------
>  mm/hugetlb_cgroup.c     |   8 +-
>  6 files changed, 294 insertions(+), 169 deletions(-)
>