On 29/10/15 10:46, Russell Coker wrote: > Package: coreutils > Version: 8.23-4 > Severity: normal > > If you copy many large files to a slow device the amount of memory used for > cache grows needlessly and impacts overall system performance. As we already > have the --reflink option I think that a precedent has been set for adding cp > options to improve system performance.
Not exactly. That option changes the end state of the copy. > Firstly I think there should be an option to call fdatasync() after completely > writing data for a file. This would reduce the amount of RAM used for write > back caching to a maximum of the size of one file, in the case where you copy > many MP4 files to an SD card that would reduce the amount of write back cache > to something like 300M instead of something large. dd has a fdatasync option > to do this. > > Next I think there should be an option to avoid caching file data which would > be particularly useful when it is known that the size of the files is larger > than the system RAM (IE caching really can't do any good even if you are > accessing the files twice). The O_DIRECT option seems good for this and it's > an option to dd so it seems that it would work well for cp. While I agree this is an issue, I'm not sure every too should get control knobs like that. There are system wide settings to control the amount of write back cache. I'm not saying cp definitely should not get such options, though it warrants discussion, and that discussion should happen at coreut...@gnu.org. thanks, Pádraig
