[PATCH linux-next] mm/madvise: allow KSM hints for process_madvise

[cgel.zte@gmail.com]

From: xu xin <xu.xin16@zte.com.cn>

The benefits of doing this are obvious because using madvise in user code
is the only current way to enable KSM, which is inconvenient for those
compiled app without marking MERGEABLE wanting to enable KSM.

Since we already have the syscall of process_madvise(), then reusing the
interface to allow external KSM hints is more acceptable [1].

Although this patch was released by Oleksandr Natalenko, but it was
unfortunately terminated without any conclusions because there was debate
on whether it should use signal_pending() to check the target task besides
the task of current() when calling unmerge_ksm_pages of other task [2].

I think it's unneeded to check the target task. For example, when we set
the klob /sys/kernel/mm/ksm/run from 1 to 2,
unmerge_and_remove_all_rmap_items() doesn't use signal_pending() to check
all other target tasks either.

I hope this patch can get attention again.

[1] https://lore.kernel.org/lkml/YoOrdh85+AqJH8w1@dhcp22.suse.cz/
[2] https://lore.kernel.org/lkml/2a66abd8-4103-f11b-06d1-07762667eee6@suse.cz/

Signed-off-by: Oleksandr Natalenko <oleksandr@redhat.com>
Signed-off-by: xu xin <xu.xin16@zte.com.cn>
---
 mm/madvise.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/madvise.c b/mm/madvise.c
index 851fa4e134bc..df915531ad9f 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1173,6 +1173,10 @@ process_madvise_behavior_valid(int behavior)
 	case MADV_COLD:
 	case MADV_PAGEOUT:
 	case MADV_WILLNEED:
+#ifdef CONFIG_KSM
+	case MADV_MERGEABLE:
+	case MADV_UNMERGEABLE:
+#endif
 		return true;
 	default:
 		return false;
-- 
2.25.1