linux-kernel - Re: [PATCH 2/4] hugetlg: Break earlier in add_reservation_in

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Message-ID: <a90497d1-5bb0-ce30-437e-41d3ffa9e12e@oracle.com>
Date:   Wed, 3 Feb 2021 16:45:03 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Peter Xu <peterx@...hat.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Cc:     Wei Zhang <wzam@...zon.com>, Matthew Wilcox <willy@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Gal Pressman <galpress@...zon.com>,
        Christoph Hellwig <hch@....de>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Jan Kara <jack@...e.cz>,
        Kirill Shutemov <kirill@...temov.name>,
        David Gibson <david@...son.dropbear.id.au>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Jann Horn <jannh@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/4] hugetlg: Break earlier in add_reservation_in_range()
 when we can

On 2/3/21 1:08 PM, Peter Xu wrote:
> All the regions maintained in hugetlb reserved map is inclusive on "from" but
> exclusive on "to".  We can break earlier even if rg->from==t because it already
> means no possible intersection.
> 
> This does not need a Fixes in all cases because when it happens (rg->from==t)
> we'll not break out of the loop while we should, however the next thing we'd do
> is still add the last file_region we'd need and quit the loop in the next
> round.  So this change is not a bugfix (since the old code should still run
> okay iiuc), but we'd better still touch it up to make it logically sane.
> 
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
>  mm/hugetlb.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index d2859c2aecc9..9e6ea96bf33b 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -377,7 +377,7 @@ static long add_reservation_in_range(struct resv_map *resv, long f, long t,
>  		/* When we find a region that starts beyond our range, we've
>  		 * finished.
>  		 */
> -		if (rg->from > t)
> +		if (rg->from >= t)
>  			break;
>  
>  		/* Add an entry for last_accounted_offset -> rg->from, and
> 

Changing any of this code makes me nervous.  However, I agree with your
analysis.  The change makes the code match the comment WRT the [from, to)
nature of regions.

Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
-- 
Mike Kravetz