What does SReclaimable in meminfo mean

Question

Slab memory in /proc/meminfo are split into SReclaimable and SUnreclaim, how can SReclaimable memory get really reclaimed and when?

Answer 1

According man proc(5):

SReclaimable %lu (since Linux 2.6.19)

Part of Slab, that might be reclaimed, such as caches.

It means that SReclaimable is memory that is used by kernel (for example, as a filesystem cache), but should any other need arise, it might be used for other purposes - for example to satisfy memory requests from user applications that cannot be satisfied otherwise, for example by using free (MemFree) memory.