Re: [PATCH v4 0/5] THP aware uprobe

[Song Liu]

On Thu, Jun 13, 2019 at 10:58 AM Song Liu <songliubraving@xxxxxx> wrote:
>
> This set makes uprobe aware of THPs.
>
> Currently, when uprobe is attached to text on THP, the page is split by
> FOLL_SPLIT. As a result, uprobe eliminates the performance benefit of THP.
>
> This set makes uprobe THP-aware. Instead of FOLL_SPLIT, we introduces
> FOLL_SPLIT_PMD, which only split PMD for uprobe. After all uprobes within
> the THP are removed, the PTEs are regrouped into huge PMD.
>
> Note that, with uprobes attached, the process runs with PTEs for the huge
> page. The performance benefit of THP is recovered _after_ all uprobes on
> the huge page are detached.
>
> This set (plus a few THP patches) is also available at
>
>    https://github.com/liu-song-6/linux/tree/uprobe-thp
>
> Changes since v3:
> 1. Simplify FOLL_SPLIT_PMD case in follow_pmd_mask(), (Kirill A. Shutemov)
> 2. Fix try_collapse_huge_pmd() to match change in follow_pmd_mask().
>
> Changes since v2:
> 1. For FOLL_SPLIT_PMD, populated the page table in follow_pmd_mask().
> 2. Simplify logic in uprobe_write_opcode. (Oleg Nesterov)
> 3. Fix page refcount handling with FOLL_SPLIT_PMD.
> 4. Much more testing, together with THP on ext4 and btrfs (sending in
>    separate set).
> 5. Rebased up on Linus's tree:
>    commit 35110e38e6c5 ("Merge tag 'media/v5.2-2' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media")
>
> Changes since v1:
> 1. introduces FOLL_SPLIT_PMD, instead of modifying split_huge_pmd*();
> 2. reuse pages_identical() from ksm.c;
> 3. rewrite most of try_collapse_huge_pmd().
>

Hi Kirill and Oleg,

Does this version look good to you? If so, could you please reply with
your Acked-by and/or Reviewed-by?

Thanks,
Song