linux-kernel - Re: [PATCH V7 2/2] mm: shmem: implement POSIX_FADV

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Date:   Thu, 18 May 2023 18:16:25 +0530
From:   Charan Teja Kalla <quic_charante@...cinc.com>
To:     Hugh Dickins <hughd@...gle.com>
CC:     <akpm@...ux-foundation.org>, <willy@...radead.org>,
        <markhemm@...glemail.com>, <rientjes@...gle.com>,
        <surenb@...gle.com>, <shakeelb@...gle.com>, <fvdl@...gle.com>,
        <quic_pkondeti@...cinc.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V7 2/2] mm: shmem: implement POSIX_FADV_[WILL|DONT]NEED
 for shmem

Hi Hugh, Thanks for the time and comments on this patch.

On 5/17/2023 5:02 PM, Hugh Dickins wrote:
>> Sure, will include those range calculations for shmem pages too.
> Oh, I forgot this issue, you would have liked me to look at V8 by now,
> to see whether I agree with your resolution there.  Sorry, no, I've
> not been able to divert my concentration to it yet.
> 
> And it's quite likely that I shall disagree, because I've a history of
> disagreeing even with myself on such range widening/narrowing issues -
> reconciling conflicting precedents is difficult :(
> 
If you can at least help by commenting which part of the patch you
disagree with, I can try hard to convince you there:) .

>> Please let me know if I'm missing something where I should be counting
>> these as NR_ISOLATED.
> Please grep for NR_ISOLATED, to see where and how they get manipulated
> already, and follow the existing examples.  The case that sticks in my
> mind is in mm/mempolicy.c, where the migrate_pages() syscall can build
> up a gigantic quantity of transiently isolated pages: your syscall can
> do the same, so should account for itself in the same way.

I had a V8 posted without this into accounting. Let me make the changes
to account for the NR_ISOLATED too.
> 
> I'm not claiming that mm/vmscan.c's too_many_isolated(), and the way it
> gets used by shrink_inactive_list(), is perfect: not at all.  But please
> follow existing convention.
> 
> Sorry, that's all for now.