diff options
Diffstat (limited to 'Documentation/sysctl/vm.txt')
| -rw-r--r-- | Documentation/sysctl/vm.txt | 56 |
1 files changed, 53 insertions, 3 deletions
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt index 774da3d5f..099d2a3b4 100644 --- a/Documentation/sysctl/vm.txt +++ b/Documentation/sysctl/vm.txt @@ -18,6 +18,7 @@ Currently, these files are in /proc/sys/vm: - bdflush - buffermem - freepages +- kswapd - overcommit_memory - pagecache - swapctl @@ -112,9 +113,58 @@ freepages: This file contains the values in the struct freepages. That struct contains three members: min, low and high. -These variables are currently unused (?), but they're -very likely to be abused for something else in the near -future, so don't yet remove it from the source... +Although the goal of the Linux memory management subsystem +is to avoid fragmentation and make large chunks of free +memory (so that we can hand out DMA buffers and such), there +still are some page-based limits in the system, mainly to +make sure we don't waste too much memory trying to get large +free area's. + +The meaning of the numbers is: + +freepages.min When the number of free pages in the system + reaches this number, only the kernel can + allocate more memory. +freepages.low If memory is too fragmented, the swapout + daemon is started, except when the number + of free pages is larger than freepages.low. +freepages.high The swapping daemon exits when memory is + sufficiently defragmented, when the number + of free pages reaches freepages.high or when + it has tried the maximum number of times. + +============================================================== + +kswapd: + +Kswapd is the kernel swapout daemon. That is, kswapd is that +piece of the kernel that frees memory when it get's fragmented +or full. Since every system is different, you'll probably want +some control over this piece of the system. + +The numbers in this page correspond to the numbers in the +struct pager_daemon {tries_base, tries_min, swap_cluster +}; The tries_base and swap_cluster probably have the +largest influence on system performance. + +tries_base The maximum number of pages kswapd tries to + free in one round is calculated from this + number. Usually this number will be divided + by 4 or 8 (see mm/vmscan.c), so it isn't as + big as it looks. + When you need to increase the bandwith to/from + swap, you'll want to increase this number. +tries_min This is the minimum number of times kswapd + tries to free a page each time it is called. + Basically it's just there to make sure that + kswapd frees some pages even when it's being + called with minimum priority. +swap_cluster This is the number of pages kswapd writes in + one turn. You want this large so that kswapd + does it's I/O in large chunks and the disk + doesn't have to seek often, but you don't want + it to be too large since that would flood the + request queue. ============================================================== |