Messages in this thread | | | Date | Thu, 16 Dec 2021 23:43:23 +0800 | Subject | Re: [PATCH 1/2] mm: add MemAvailable to per-node meminfo | From | Qi Zheng <> |
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On 12/16/21 11:37 PM, Greg KH wrote: > On Thu, Dec 16, 2021 at 11:31:36PM +0800, Qi Zheng wrote: >> >> >> On 12/16/21 9:16 PM, Greg KH wrote: >>> On Thu, Dec 16, 2021 at 08:46:54PM +0800, Qi Zheng wrote: >>>> In /proc/meminfo, we can show the sum of all the available memory >>>> as "MemAvailable". Add the same counter also to per-node meminfo >>>> under /sys. >>>> >>>> With this counter, some processes that bind nodes can make some >>>> decisions by reading the "MemAvailable" of the corresponding nodes >>>> directly. >>>> >>>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com> >>>> --- >>>> drivers/base/node.c | 4 ++++ >>>> include/linux/mm.h | 1 + >>>> include/linux/mmzone.h | 5 +++++ >>>> mm/page_alloc.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++ >>>> 4 files changed, 59 insertions(+) >>>> >>>> diff --git a/drivers/base/node.c b/drivers/base/node.c >>>> index 87acc47e8951..deb2a7965ae4 100644 >>>> --- a/drivers/base/node.c >>>> +++ b/drivers/base/node.c >>>> @@ -375,8 +375,10 @@ static ssize_t node_read_meminfo(struct device *dev, >>>> struct sysinfo i; >>>> unsigned long sreclaimable, sunreclaimable; >>>> unsigned long swapcached = 0; >>>> + long available; >>>> si_meminfo_node(&i, nid); >>>> + available = si_mem_available_node(&i, nid); >>>> sreclaimable = node_page_state_pages(pgdat, NR_SLAB_RECLAIMABLE_B); >>>> sunreclaimable = node_page_state_pages(pgdat, NR_SLAB_UNRECLAIMABLE_B); >>>> #ifdef CONFIG_SWAP >>>> @@ -386,6 +388,7 @@ static ssize_t node_read_meminfo(struct device *dev, >>>> "Node %d MemTotal: %8lu kB\n" >>>> "Node %d MemFree: %8lu kB\n" >>>> "Node %d MemUsed: %8lu kB\n" >>>> + "Node %d MemAvailable: %8lu kB\n" >>> >>> You just changed a user/kernel api without documenting it anywhere, or >>> ensuring that you did not just break anything. >> >> Hi greg k-h, >> >> The MemAvailable has long existed in the /proc/meminfo, it's meaning >> has been described in the Documentation/filesystems/proc.rst. Since >> the semantics of per-node MemAvailable has not changed, so I did not >> add a new document description. > > This is not a proc file, it is in sysfs. > > And it violates all of the sysfs rules, and has all of the problems that > proc files have. So the worst of both worlds :( > >>> Also, this api is crazy, and not ok, please never add anything new to >>> it, it is broken as-is. >> >> The consideration of adding per-node MemAvailable is that some processes >> that bind nodes need this information to do some decisions. >> >> Now their approach is to read other information in per-node meminfo >> and /proc/sys/vm/watermark_scale_factor, and then approximate this >> value. With this counter, they can directly read >> /sys/devices/system/node/node*/meminfo to get the MemAvailable >> information of each node. >> >> And MemTotal, MemFree and SReclaimable(etc.) all have corresponding >> per-node versions, so I think that adding per-node MemAvailable might >> also make sense. :) > > Please no, I do not want new things added to this file, as you might > break parsers of this file.
OK, Got it.
Thank, Qi
> > Also, again, you did not document this at all in Documentation/ABI/ so > for that reason alone it is not ok. > > thanks, > > greg k-h >
-- Thanks, Qi
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