On Tue, 30 Jun 2015, Simmons, James A. wrote: > >Yeah. You're right. Doing a vmalloc() when kmalloc() doesn't have even > >a tiny sliver of RAM isn't going to work. It's easier to use > >libcfs_kvzalloc() everywhere, but it's probably the wrong thing. > > The original reason we have the vmalloc water mark wasn't so much the > issue of memory exhaustion but to handle the case of memory fragmentation. > Some sites had after a extended period of time started to see failures of > allocating even 32K using kmalloc. In our latest development branch we moved > away from using a water mark to always try kmalloc first and if it fails then we > try vmalloc. At ORNL we ran into severe performance issues when we entered > vmalloc territory. It has been discussed before on what might replace vmalloc > handling in the case of kmalloc fails but no solution has been worked out. OK, but if a structure contains only 4 words, would it be better to just use kzalloc? Or does it not matter? It would only save trying vmalloc in a case that it is guaranteed to fail, but if a structure with 4 words can't be allocatted, the system has other problems. Another argument is that kzalloc is a well known function that people and bug-finding tools understand, so it is better to use it whenever possible. Some of the other structures contain a lot more fields, as well as small arrays. They are probably acceptable for kzalloc too, but I wouldn't know the exact dividing line. julia -- To unsubscribe from this list: send the line "unsubscribe kernel-janitors" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
