linux-kernel - Re: [PATCH v10 13/69] mm/mmap: use maple tree for unmapped_area{

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Message-ID: <20220719145415.dvtpwfykfmddi4sx@revolver>
Date:   Tue, 19 Jul 2022 14:54:21 +0000
From:   Liam Howlett <liam.howlett@...cle.com>
To:     Sven Schnelle <svens@...ux.ibm.com>
CC:     "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>,
        "damon @ lists . linux . dev" <damon@...ts.linux.dev>,
        SeongJae Park <sj@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        "hca@...ux.ibm.com" <hca@...ux.ibm.com>,
        "alexander.gordeev@...ux.ibm.com" <alexander.gordeev@...ux.ibm.com>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>
Subject: Re: [PATCH v10 13/69] mm/mmap: use maple tree for
 unmapped_area{_topdown}

* Sven Schnelle <svens@...ux.ibm.com> [220719 10:21]:
> Hi Liam,
> 
> Liam Howlett <liam.howlett@...cle.com> writes:
> 
> > From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
> >
> > The maple tree code was added to find the unmapped area in a previous
> > commit and was checked against what the rbtree returned, but the actual
> > result was never used.  Start using the maple tree implementation and
> > remove the rbtree code.
> >
> > Add kernel documentation comment for these functions.
> >
> > Link: https://lkml.kernel.org/r/20220504010716.661115-15-Liam.Howlett@oracle.com
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> > Cc: Catalin Marinas <catalin.marinas@....com>
> > Cc: David Howells <dhowells@...hat.com>
> > Cc: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> > Cc: SeongJae Park <sj@...nel.org>
> > Cc: Vlastimil Babka <vbabka@...e.cz>
> > Cc: Will Deacon <will@...nel.org>
> > Cc: Davidlohr Bueso <dave@...olabs.net>
> > Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> > ---
> >  mm/mmap.c | 253 +++++++-----------------------------------------------
> >  1 file changed, 32 insertions(+), 221 deletions(-)
> 
> With next-20220718 git bisect pointed me to this commit because the
> following code fails in compat mode (31 bit addressing) on s390:
> 
> #include <unistd.h>
> #include <stdlib.h>
> #include <sys/mman.h>
> #include <stdio.h>
> 
> #define __2GB__         0x80000000
> #define VMA_SIZE        0x10000000
> #define VMA_COUNT       (__2GB__ / VMA_SIZE)
> 
> /*
>  * Repeated mapping below 2GB until all memory is exhausted
>  */
> int main(void)
> {
>         void *p;
>         unsigned int i;
> 
>         for (i = 0; i < VMA_COUNT; i++) {
>             p = mmap(NULL, VMA_SIZE, PROT_READ,MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
>             printf("%d: %08x - %08x\n", i, (int)p, (int)p + VMA_SIZE);
>             if (p == MAP_FAILED)
>                   break;
>             if (p > (void *)__2GB__) {
>                   return 1;
>             }
>         }
>         if ((i == 0) || (i >= VMA_COUNT))
>                return 2;
>         return 0;
> }
> 
> With linux/master:
> # ./mmap_compat_anon
> 0: 67a00000 - 77a00000
> 1: 57a00000 - 67a00000
> 2: 47a00000 - 57a00000
> 3: 37a00000 - 47a00000
> 4: 27a00000 - 37a00000
> 5: 17a00000 - 27a00000
> 6: 07a00000 - 17a00000
> 7: ffffffff - 0fffffff
> 
> With next-20220718 (and older, we're seeing this for a while, but i
> didn't notice due to vacation and other priorities):
> 
> # ./mmap_compat_anon
> 0: 67600000 - 77600000
> 1: 57600000 - 67600000
> 2: 47600000 - 57600000
> 3: 37600000 - 47600000
> 4: 27600000 - 37600000
> 5: 17600000 - 27600000
> 6: 07600000 - 17600000
> 7: 40000000 - 50000000
> 
> So the first output is correct - mmap succeeds until there's no space
> left, where it returns MAP_FAILED. In the lower (failing) one, mmap
> instead returns an address that is already in use.
> 

I'll have a look.

Thanks,
Liam