Le lun. 23 mars 2026 à 14:23, Pádraig Brady <[email protected]> a écrit : > > On 08/03/2026 12:11, Laurent Lyaudet wrote: > > Hello :), > > > > I'm not an expert of kernel and architecture, > > but I do know some things. > > For example, I know that Linux keeps frequently accessed files in RAM, > > and that when writing there are options to ensure that > > the write finishes only when the file was modified on the HDD, SSD. > > (More or less since there is a cache also at the SSD, > > and if I remember correctly, > > databases software editors sell servers with a custom OS, > > an enormous amount of RAM and their software > > to bring better guarantees to the security/validity of data (in case > > of failure)). > > > > When coding bash scripts, > > I saw (without precise measure) > > that my code executed faster when I merged consecutive commands into one. > > In particular for sed (using repeated -e) > > that, I admit, is not in coreutils, > > a single sed command was faster than > > consecutive sed commands. > > > > I do know that it is something that is well-known, > > since it is the reason it is recommended to use Bash or other shells > > builtins, when possible, instead of spawning a new process. > > > > But I wondered : > > - if the cost is mainly to copy the code in machine language > > (executable, ELF in case of Linux) to the RAM or the cache, > > - and if so if there was something in Linux or on some CPUs > > (AMD?, Intel?, server CPUs?) such that some files can be kept "forever" > > in L3 Cache since today CPUs L3 Cache is enormous on some > > CPUs, it would logic that the kernel and the core utils > > are never removed from the L3 cache to go the RAM. > > It's kind of a mixte mode between Von Neumann architecture > > and Harvard architecture, > > where executable code compared to data would have > > a privileged mode to stay in cache. > > > > Does anybody knows if such a thing exists ? > > If not, I think it would be a good idea FOR PERFORMANCE. > > It may be a bad idea for SECURITY > > because the addresses would always be the same > > (I'm not an expert of that, that's just my "general specialized" culture > > in informatics that makes me think that.) > > Yes there are two main costs. > 1. Loading pages from persistent storage. > 2. Setting up the initial state in the process. > Both are significant. > > You could avoid 1. with something like: > > vmtouch -l $(rpm -ql coreutils | grep bin/) > > cheers, > Padraig
Hello Padraig, Thanks for your attempt to answer. But I was talking about L3 Cache of CPU, from what I can see here : https://hoytech.com/vmtouch/ https://github.com/hoytech/vmtouch/blob/master/vmtouch.pod vmtouch only deals with RAM cache of filesystem, not L3 CPU cache. I already talked of the RAM cache of filesystem in my previous email. I knew about it and that there could still be a performance difference with L3 cache. Best regards, Laurent Lyaudet
