>> >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 allocated, 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. The reason I bring this up is to discuss sorting this out. Once long ago we had just LIBCFS_ALLOC. For some reason before my time OBD_ALLOC got spawned off of that. Currently LIBCFS_ALLOC is used just by the libcfs/LNet layer. Now OBD_ALLOC in our development branch has moved to a try kmalloc first and if it fails try vmalloc for any size memory allocation. LIBCFS_ALLOC still does the original approach. So we have two possible solutions depending on if libcfs/LNet needs to ever do a vmalloc. One solution if libcfs/LNet never needs a vmalloc is remove LIBCFS_ALLOC and replace it with kzalloc everywhere. We can then move libcfs_kzvalloc to the lustre layer and port the change we did in the development branch to here of the try kmalloc then vmalloc approach. The other approach is if libcfs/LNet does in some case need to use vmalloc we could then update LIBCFS_ALLOC to first try kmalloc then vmalloc. Once this is implemented we can nuke the OBD_ALLOC system. Either way I like to see it consolidated down to one system. -- 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
