From: Robert Ho <robert.hu@xxxxxxxxx> Subject: Documentation/filesystems/proc.txt: add more description for maps/smaps Add some more description on the limitations for smaps/maps readings, as well as some guaruntees we can make. Link: http://lkml.kernel.org/r/1475296958-27652-2-git-send-email-robert.hu@xxxxxxxxx Signed-off-by: Robert Ho <robert.hu@xxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxx> Cc: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx> Cc: Robert Hu <robert.hu@xxxxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> Cc: Gleb Natapov <gleb@xxxxxxxxxx> Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx> Cc: Stefan Hajnoczi <stefanha@xxxxxxxxxx> Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- Documentation/filesystems/proc.txt | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff -puN Documentation/filesystems/proc.txt~dcumentation-filesystems-proctxt-add-more-description-for-maps-smaps Documentation/filesystems/proc.txt --- a/Documentation/filesystems/proc.txt~dcumentation-filesystems-proctxt-add-more-description-for-maps-smaps +++ a/Documentation/filesystems/proc.txt @@ -515,6 +515,18 @@ be vanished or the reverse -- new added. This file is only present if the CONFIG_MMU kernel configuration option is enabled. +Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy (consistent +output can be achieved only in the single read call). +This typically manifests when doing partial reads of these files while the +memory map is being modified. Despite the races, we do provide the following +guarantees: + +1) The mapped addresses never go backwards, which implies no two + regions will ever overlap. +2) If there is something at a given vaddr during the entirety of the + life of the smaps/maps walk, there will be some output for it. + + The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG bits on both physical and virtual pages associated with a process, and the soft-dirty bit on pte (see Documentation/vm/soft-dirty.txt for details). _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
