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mm/vmalloc.c: find the vmap of vmap_nodes in reverse order

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When finding VA in vn->busy, if VA spans several zones and the passed addr
is not the same as va->va_start, we should scan the vn in reverse odrdr
because the starting address of VA must be smaller than the passed addr if
it really resides in the VA.

E.g on a system nr_vmap_nodes=100,

     <----va---->
 -|-----|-----|-----|-----|-----|-----|-----|-----|-----|-
    ...   n-1   n    n+1   n+2   ...   100     0     1

VA resides in node 'n' whereas it spans 'n', 'n+1' and 'n+2'.  If passed
addr is within 'n+2', we should try nodes backwards on 'n+1' and 'n', then
succeed very soon.

Meanwhile we still need loop around because VA could spans node from 'n'
to node 100, node 0, node 1.

Anyway, changing to find in reverse order can improve efficiency on many
CPUs system.

Link: https://lkml.kernel.org/r/20250418223653.243436-3-bhe@redhat.com
Signed-off-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Shivank Garg <shivankg@amd.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Baoquan He
2025-04-19 06:36:50 +08:00
committed by Andrew Morton
parent f7f68274e4
commit 81262d85ae
1 changed files with 2 additions and 2 deletions
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4
mm/vmalloc.c
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@@ -2435,7 +2435,7 @@ struct vmap_area *find_vmap_area(unsigned long addr)
if (va)
return va;
} while ((i = (i + 1) % nr_vmap_nodes) != j);
} while ((i = (i + nr_vmap_nodes - 1) % nr_vmap_nodes) != j);
return NULL;
}
@@ -2461,7 +2461,7 @@ static struct vmap_area *find_unlink_vmap_area(unsigned long addr)
if (va)
return va;
} while ((i = (i + 1) % nr_vmap_nodes) != j);
} while ((i = (i + nr_vmap_nodes - 1) % nr_vmap_nodes) != j);
return NULL;
}