From: Charan Teja Kalla quic_charante@quicinc.com Subject: mm: madvise: return correct bytes advised with process_madvise

Patch series "mm: madvise: return correct bytes processed with process_madvise", v2. With the process_madvise(), always choose to return non zero processed bytes over an error. This can help the user to know on which VMA, passed in the 'struct iovec' vector list, is failed to advise thus can take the decission of retrying/skipping on that VMA.

This patch (of 2):

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.

Link: https://lkml.kernel.org/r/cover.1647008754.git.quic_charante@quicinc.com Link: https://lkml.kernel.org/r/125b61a0edcee5c2db8658aed9d06a43a19ccafc.164700875... Fixes: ecb8ac8b1f14("mm/madvise: introduce process_madvise() syscall: an external memory hinting API") Signed-off-by: Charan Teja Kalla quic_charante@quicinc.com Cc: Suren Baghdasaryan surenb@google.com Cc: Vlastimil Babka vbabka@suse.cz Cc: David Rientjes rientjes@google.com Cc: Stephen Rothwell sfr@canb.auug.org.au Cc: Minchan Kim minchan@kernel.org Cc: Nadav Amit nadav.amit@gmail.com Cc: Michal Hocko mhocko@suse.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/madvise.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/mm/madvise.c~mm-madvise-return-correct-bytes-advised-with-process_madvise +++ a/mm/madvise.c @@ -1435,8 +1435,7 @@ SYSCALL_DEFINE5(process_madvise, int, pi iov_iter_advance(&iter, iovec.iov_len); }

- if (ret == 0) - ret = total_len - iov_iter_count(&iter); + ret = (total_len - iov_iter_count(&iter)) ? : ret;

release_mm: mmput(mm); _