Re: [PATCH v7 26/70] mm/mmap: Use advanced maple tree API for mmap_region()

Andrew Morton
2022-04-14T06:51:18Z

On Mon, 4 Apr 2022 14:35:43 +0000 Liam Howlett <liam.howlett@oracle.com> wrote:

> From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>
>
> Changing mmap_region() to use the maple tree state and the advanced
> maple tree interface allows for a lot less tree walking.
>
> This change removes the last caller of munmap_vma_range(), so drop this
> unused function.
>
> Add vma_expand() to expand a VMA if possible by doing the necessary
> hugepage check, uprobe_munmap of files, dcache flush, modifications then
> undoing the detaches, etc.
>

Merging this with Yang Shi's "mm: mmap: register suitable readonly file
vmas for khugepaged"
(https://lkml.kernel.org/r/20220404200250.321455-9-shy828301@gmail.com)

> ...
>
> @@ -1741,13 +1868,28 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> goto free_vma;
> }
>
> - vma_link(mm, vma, prev);
> + if (vma->vm_file)
> + i_mmap_lock_write(vma->vm_file->f_mapping);
> +
> + vma_mas_store(vma, &mas);
> + __vma_link_list(mm, vma, prev);
> + mm->map_count++;
> + if (vma->vm_file) {
> + if (vma->vm_flags & VM_SHARED)
> + mapping_allow_writable(vma->vm_file->f_mapping);
> +
> + flush_dcache_mmap_lock(vma->vm_file->f_mapping);
> + vma_interval_tree_insert(vma, &vma->vm_file->f_mapping->i_mmap);
> + flush_dcache_mmap_unlock(vma->vm_file->f_mapping);
> + i_mmap_unlock_write(vma->vm_file->f_mapping);
> + }
> +
> /* Once vma denies write, undo our temporary denial count */
> unmap_writable:
> if (file && vm_flags & VM_SHARED)
> mapping_unmap_writable(file->f_mapping);

I'm unsure whether this hunk should be inside or outside the call to
the cheerfully undocumented khugepaged_enter_vma()?

Code snippet as I presently have it:

if (vma->vm_file)
i_mmap_lock_write(vma->vm_file->f_mapping);

vma_mas_store(vma, &mas);
mm->map_count++;
if (vma->vm_file) {
if (vma->vm_flags & VM_SHARED)
mapping_allow_writable(vma->vm_file->f_mapping);

flush_dcache_mmap_lock(vma->vm_file->f_mapping);
vma_interval_tree_insert(vma, &vma->vm_file->f_mapping->i_mmap);
flush_dcache_mmap_unlock(vma->vm_file->f_mapping);
i_mmap_unlock_write(vma->vm_file->f_mapping);
}

/*
* vma_merge() calls khugepaged_enter_vma() either, the below
* call covers the non-merge case.
*/
khugepaged_enter_vma(vma, vma->vm_flags);

/* Once vma denies write, undo our temporary denial count */
unmap_writable:
if (file && vm_flags & VM_SHARED)
mapping_unmap_writable(file->f_mapping);

btw, "vma_merge() calls khugepaged_enter_vma() either" isn't
understandable. Should that be "also"?