On 27/06/11 11:29, Andrea Righi wrote: > The actual problem I think is that apps expect that DONTNEED can be used > to drop cache, but this is not written anywhere in the POSIX standard. > > I would also like to have both functionalities: 1) be sure to drop page > cache pages (now there's only a system-wide knob to do this: > /proc/sys/vm/drop_caches), 2) give an advice to the kernel that I will > not reuse some pages in the future. > > The standard can only provide 2). If we also want 1) at the file > granularity, I think we'd need to introduce something linux specific to > avoid having portability problems. True, though Linux is the reference for posix_fadvise() implementations, given its lack of support on other platforms. So just to summarize for _my_ reference. You're changing DONTNEED to mean "drop if !PageActive()". I.E. according to http://linux-mm.org/PageReplacementDesign "drop if files only accessed once". This will mean that there is no way currently to remove a particular file from the cache on linux. Hopefully that won't affect any of: http://codesearch.google.com/#search/&q=POSIX_FADV_DONTNEED Ideally I'd like cache functions for: DROP, ADD, ADD if space¹ which could correspond to: DONTNEED, WILLNEED, NOREUSE but what we're going for are these somewhat overlapping functions: DROP if used once², ADD, ADD if space cheers, Pádraig. ¹ Not implemented yet. ² Hopefully there are no access patterns a single process can do to make a PageActive as that would probably not be desired in relation to "Drop if used once" functionality. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>