On Tue, Jul 21, 2015 at 4:34 PM, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > On Sun, 19 Jul 2015 15:31:09 +0300 Vladimir Davydov <vdavydov@xxxxxxxxxxxxx> wrote: >> To mark a page idle one should set the bit corresponding to the >> page by writing to the file. A value written to the file is OR-ed with the >> current bitmap value. Only user memory pages can be marked idle, for other >> page types input is silently ignored. Writing to this file beyond max PFN >> results in the ENXIO error. Only available when CONFIG_IDLE_PAGE_TRACKING is >> set. >> >> This file can be used to estimate the amount of pages that are not >> used by a particular workload as follows: >> >> 1. mark all pages of interest idle by setting corresponding bits in the >> /proc/kpageidle bitmap >> 2. wait until the workload accesses its working set >> 3. read /proc/kpageidle and count the number of bits set > > Security implications. This interface could be used to learn about a > sensitive application by poking data at it and then observing its > memory access patterns. Perhaps this is why the proc files are > root-only (whcih I assume is sufficient). Some words here about the > security side of things and the reasoning behind the chosen permissions > would be good to have. As long as this stays true-root-only, I think it should be safe enough. >> * /proc/kpagecgroup. This file contains a 64-bit inode number of the >> memory cgroup each page is charged to, indexed by PFN. > > Actually "closest online ancestor". This also should be in the > interface documentation. > >> Only available when CONFIG_MEMCG is set. > > CONFIG_MEMCG and CONFIG_IDLE_PAGE_TRACKING I assume? > >> >> This file can be used to find all pages (including unmapped file >> pages) accounted to a particular cgroup. Using /proc/kpageidle, one >> can then estimate the cgroup working set size. >> >> For an example of using these files for estimating the amount of unused >> memory pages per each memory cgroup, please see the script attached >> below. > > Why were these put in /proc anyway? Rather than under /sys/fs/cgroup > somewhere? Presumably because /proc/kpageidle is useful in non-memcg > setups. Do we need a /proc/vm/ for holding these kinds of things? We're collecting a lot there. Or invent some way for this to be sensible in /sys? -Kees -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
