linux-kernel - Re: [PATCH] mm: Remove VM_BUG_ON in __alloc_pages

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Date:   Wed, 5 Jun 2019 18:37:28 +0530
From:   Bharath Vedartham <linux.bhar@...il.com>
To:     Michal Hocko <mhocko@...nel.org>, akpm@...ux-foundation.org,
        vbabka@...e.cz, rientjes@...gle.com
Cc:     khalid.aziz@...cle.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: Remove VM_BUG_ON in __alloc_pages_node

[Not replying inline as my mail is bouncing back]

This patch is based on reading the code rather than a kernel crash. My
thought process was that if an invalid node id was passed to
__alloc_pages_node, it would be better to add a VM_WARN_ON and fail the
allocation rather than crashing the kernel. 
I feel it would be better to fail the allocation early in the hot path
if an invalid node id is passed. This is irrespective of whether the
VM_[BUG|WARN]_*s are enabled or not. I do not see any checks in the hot
path for the node id, which in turn may cause NODE_DATA(nid) to fail to
get the pglist_data pointer for the node id. 
We can optimise the branch by wrapping it around in unlikely(), if
performance is the issue?
What are your thoughts on this? 

Thank you 
Bharath