linux-kernel - Re: [PATCH] mm: remove lru_add_drain_all in alloc_contig

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Date:   Wed, 10 Feb 2021 13:23:10 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Oscar Salvador <osalvador@...e.de>,
        David Hildenbrand <david@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: remove lru_add_drain_all in alloc_contig_range

On Wed 10-02-21 13:17:33, Vlastimil Babka wrote:
> On 2/9/21 8:03 PM, Oscar Salvador wrote:
> > On Tue, Feb 09, 2021 at 07:17:59PM +0100, David Hildenbrand wrote:
> >> I was expecting some magical reason why this is still required but I am not
> >> able to find a compelling one. Maybe this is really some historical
> >> artifact.
> >> 
> >> Let's see if other people know why this call here still exists.
> > 
> > I also stumbled upon this while working on adding hugetlb support for
> > alloc_acontig_range [1].
> > I have to confess I puzzled me a bit.
> > 
> > I saw it going back to when the function was first introduced by 
> > 
> > commit 041d3a8cdc18dc375a128d90bbb753949a81b1fb
> > Author: Michal Nazarewicz <mina86@...a86.com>
> > Date:   Thu Dec 29 13:09:50 2011 +0100
> > 
> >     mm: page_alloc: introduce alloc_contig_range()
> > 
> > 
> > It does not make much sense to me. At this point our pages are free, so
> > we do not care about LRU handling here.
> > But I might be missing something.
> 
> AFAICS, at the time page migration used putback_lru_page() to release the
> migration source page. This would put the page on lru pvec even if it was in
> fact not mapped anywhere anymore, and only the drain would actually free it.
> Seems Minchan optimized this in 2016 by c6c919eb90e0 ("mm: use put_page() to
> free page instead of putback_lru_page()")

This would be a great addition to the changelog. Thanks a lot Vlastimil,
you saved me from some archeology. With that mentioned feel free to add

Acked-by: Michal Hocko <mhocko@...e.com>

> 
> > [1] https://lore.kernel.org/linux-mm/20210208103935.GA32103@linux/T/#md651fc6e73c656105179382f92f8b2d6073051d1
> > 
> > 
> 

-- 
Michal Hocko
SUSE Labs