linux-kernel - Re: [PATCH V2,1/2] mm: madvise: return correct bytes advised with process

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Date:   Tue, 15 Mar 2022 15:20:52 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     Charan Teja Kalla <quic_charante@...cinc.com>
Cc:     akpm@...ux-foundation.org, surenb@...gle.com, vbabka@...e.cz,
        rientjes@...gle.com, sfr@...b.auug.org.au, edgararriaga@...gle.com,
        nadav.amit@...il.com, mhocko@...e.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, "# 5 . 10+" <stable@...r.kernel.org>
Subject: Re: [PATCH V2,1/2] mm: madvise: return correct bytes advised with
 process_madvise

On Fri, Mar 11, 2022 at 08:59:05PM +0530, Charan Teja Kalla wrote:
> The process_madvise() system call returns error even after processing
> some VMA's passed in the 'struct iovec' vector list which leaves the
> user confused to know where to restart the advise next. It is also
> against this syscall man page[1] documentation where it mentions that
> "return value may be less than the total number of requested bytes, if
> an error occurred after some iovec elements were already processed.".
> 
> Consider a user passed 10 VMA's in the 'struct iovec' vector list of
> which 9 are processed but one. Then it just returns the error caused on
> that failed VMA despite the first 9 VMA's processed, leaving the user
> confused about on which VMA it is failed. Returning the number of bytes
> processed here can help the user to know which VMA it is failed on and
> thus can retry/skip the advise on that VMA.
> 
> [1]https://man7.org/linux/man-pages/man2/process_madvise.2.html.
> 
> Fixes: ecb8ac8b1f14("mm/madvise: introduce process_madvise() syscall: an external memory hinting API")
> Cc: <stable@...r.kernel.org> # 5.10+
> Signed-off-by: Charan Teja Kalla <quic_charante@...cinc.com>
Acked-by: Minchan Kim <minchan@...nel.org>