linux-kernel - Re: [patch 163/227] mm: madvise: skip unmapped vma holes passed to process

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Date:   Wed, 23 Mar 2022 21:17:47 +0530
From:   Charan Teja Kalla <quic_charante@...cinc.com>
To:     Michal Hocko <mhocko@...e.com>, <linux-kernel@...r.kernel.org>
CC:     Andrew Morton <akpm@...ux-foundation.org>, <vbabka@...e.cz>,
        <surenb@...gle.com>, <stable@...r.kernel.org>,
        <sfr@...b.auug.org.au>, <rientjes@...gle.com>,
        <nadav.amit@...il.com>, <patches@...ts.linux.dev>,
        <linux-mm@...ck.org>, <mm-commits@...r.kernel.org>,
        <torvalds@...ux-foundation.org>
Subject: Re: [patch 163/227] mm: madvise: skip unmapped vma holes passed to
 process_madvise



On 3/23/2022 1:58 PM, Michal Hocko wrote:
> On Tue 22-03-22 17:24:58, Minchan Kim wrote:
>> On Tue, Mar 22, 2022 at 02:46:48PM -0700, Andrew Morton wrote:
>>> From: Charan Teja Kalla <quic_charante@...cinc.com>
>>> Subject: mm: madvise: skip unmapped vma holes passed to process_madvise
>>>
>>> The process_madvise() system call is expected to skip holes in vma passed
>>> through 'struct iovec' vector list.  But do_madvise, which
>>> process_madvise() calls for each vma, returns ENOMEM in case of unmapped
>>> holes, despite the VMA is processed.
>>>
>>> Thus process_madvise() should treat ENOMEM as expected and consider the
>>> VMA passed to as processed and continue processing other vma's in the
>>> vector list.  Returning -ENOMEM to user, despite the VMA is processed,
>>> will be unable to figure out where to start the next madvise.
>>>
>>> Link: https://lkml.kernel.org/r/4f091776142f2ebf7b94018146de72318474e686.1647008754.git.quic_charante@quicinc.com
>> I thought it was still under discussion and Charan will post next
>> version along with previous patch
>> "mm: madvise: return correct bytes advised with process_madvise"
>>
>> https://lore.kernel.org/linux-mm/7207b2f5-6b3e-aea4-aa1b-9c6d849abe34@quicinc.com/
> Yes, I am not even sure the new semantic is sensible[1]. We should discuss
> that and see all the consequences. Changing the semantic of an existing
> syscall is always tricky going back and forth is even worse.

Starting the discussion @
https://lore.kernel.org/linux-mm/cover.1648046642.git.quic_charante@quicinc.com/

Thanks,
Charan