linux-kernel - Re: [PATCH] fs/proc/base: use maple tree iterators in place of linked list

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Date:   Thu, 25 Aug 2022 16:58:24 +0000
From:   Liam Howlett <liam.howlett@...cle.com>
To:     "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] fs/proc/base: use maple tree iterators in place of linked
 list

* Davidlohr Bueso <dave@...olabs.net> [220825 12:19]:
> On Wed, 24 Aug 2022, Liam Howlett wrote:
> 
> > From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
> > 
> > Use mas_for_each to iterate the list of VMAs instead of a for loop
> > across the linked list.
> 
> Hmm so why isn't this using the standard VMA_ITERATOR?

the VMA_ITERATOR is for the easy cases.  This one was probably skipped
due to the pos = 2 in the for loop and the unknown mm_struct.  I worked
around that in my patch and I think we could switch to the vma iterator,
but it won't be any better than what is there now.  We will need to
declare the struct and call vma_iter_init() once the mm_struct is known.
It would get rid of the ULONG_MAX in the mas_for_each() line though.

> 
> > 
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> > ---
> > fs/proc/base.c | 5 ++++-
> > 1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/proc/base.c b/fs/proc/base.c
> > index 93f7e3d971e4..0b72a6d8aac3 100644
> > --- a/fs/proc/base.c
> > +++ b/fs/proc/base.c
> > @@ -2350,6 +2350,7 @@ proc_map_files_readdir(struct file *file, struct dir_context *ctx)
> > 	GENRADIX(struct map_files_info) fa;
> > 	struct map_files_info *p;
> > 	int ret;
> > +	MA_STATE(mas, NULL, 0, 0);
> > 
> > 	genradix_init(&fa);
> > 
> > @@ -2377,6 +2378,7 @@ proc_map_files_readdir(struct file *file, struct dir_context *ctx)
> > 	}
> > 
> > 	nr_files = 0;
> > +	mas.tree = &mm->mm_mt;
> > 
> > 	/*
> > 	 * We need two passes here:
> > @@ -2388,7 +2390,8 @@ proc_map_files_readdir(struct file *file, struct dir_context *ctx)
> > 	 * routine might require mmap_lock taken in might_fault().
> > 	 */
> > 
> > -	for (vma = mm->mmap, pos = 2; vma; vma = vma->vm_next) {
> > +	pos = 2;
> > +	mas_for_each(&mas, vma, ULONG_MAX) {
> > 		if (!vma->vm_file)
> > 			continue;
> > 		if (++pos <= ctx->pos)
> > -- 
> > 2.35.1