![]() ![]() Even so, I currently have 500MB reclaimable slab memory on my laptop (out of 8GB of RAM). "The impact of those factors will vary from system to system".įor many PC workloads, the point about "lots of files" might not be relevant. It might not allow enough, or it might be over-generous. So MemAvailable is allowing a small percentage of RAM for this. Otherwise, at best you will suffer delays, at worst the system will spend all its time thrashing between different applications. When you are running firefox with around 100MB of program code mapped in the page cache, you generally want to keep that 100MB in RAM :-). ![]() So if you only want a rough estimate, you can ignore this part :-). The kernel's "low watermark" can be tuned, but it is usually around 2% of system RAM. (It makes the same assumption for reclaimable slabs as well). Or half of the current cache - whichever is smaller. This MemAvailable calculation also assumes that you want to keep at least enough file cache to equal the kernel's "low watermark". (I noticed these same page counts are also used in the code that calculates the "dirty limit"). So the size of the "file LRU lists" does not include shared memory or any other swappable memory. Each 1GB increase in Shmem reduced MemAvailable by 1GB. However, I found it correctly treats Shmem as "used" memory. Pagecache -= min(pagecache / 2, wmark_low) * low watermark worth of cache, needs to stay. Assume at least half of the page cache, or the * Not all the page cache can be freed, otherwise the system will At first glance, the code did not seem to mention this distinction. I had to double-check how MemAvailable works. You might even have chosen to run without swap space, or allowed only a relatively limited amount. MemAvailable deliberately does not include swappable memory. Shmem can also include some graphics memory allocations, which could be very large. If you have too many files in a tmpfs, it could be occupying a lot of your memory :-). Cached in /proc/meminfo can be very misleading, due to including this swappable Shmem memory. MemAvailable detailsĪs it says above, tmpfs and other Shmem memory cannot be freed, only moved to swap. Impact of those factors will vary from system to system. Slab will be reclaimable, due to items being in use. ![]() Page cache to function well, and that not all reclaimable The estimate takes into account that the system needs some SReclaimable, the size of the file LRU lists, and the low MemAvailable: An estimate of how much memory is available forĪpplications, without swapping. If things change in theįuture, we only have to change it in one place. Provide such an estimate in /proc/meminfo. Really should not be expected to know kernel internals to come up withĪn estimate for the amount of free memory. However, this may change in the future, and user space Inactive(file), and SReclaimable, as well as the "low" watermarks from System into swap, can be estimated from MemFree, Active(file), Memory that is available for a new workload, without pushing the Slab memory, which can take up a large fraction of system memory on Memory segments, tmpfs, and ramfs, and it does not include reclaimable Includes memory that is not freeable as page cache, for example shared Pretty much guaranteed to be wrong today. They generally do thisīy adding up "free" and "cached", which was fine ten years ago, but is To estimate how much free memory is available. Many load balancing and workload placing programs check /proc/meminfo proc/meminfo: provide estimated available memory This value is significantly different from MemFree + Cached. The kernel now provides an estimate for available memory, in the MemAvailable field. That view can be very misleading in a number of real-world cases.
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