On 11/21, Matthew Wilcox wrote: > On Fri, Nov 21, 2025 at 07:52:02PM +0000, Jaegeuk Kim wrote: > > On 11/21, Jaegeuk Kim wrote: > > > On 11/21, Matthew Wilcox wrote: > > > > On Fri, Nov 21, 2025 at 04:46:14AM +0000, Jaegeuk Kim wrote: > > > > > On 11/21, Matthew Wilcox wrote: > > > > > > On Fri, Nov 21, 2025 at 03:27:18AM +0000, Jaegeuk Kim wrote: > > > > > > > This patch introduces a new POSIX_FADV_MLOCK which 1) invalidates > > > > > > > the range of > > > > > > > cached pages, 2) sets the mapping as inaccessible, 3) > > > > > > > POSIX_FADV_WILLNEED loads > > > > > > > pages directly to the inaccessible mapping. > > > > > > > > > > > > ... what? > > > > > > > > > > > > This seems like something which is completely different from > > > > > > mlock(). > > > > > > So it needs a different name. > > > > > > > > > > > > But I don't understand the point of this, whatever it's called. > > > > > > Need > > > > > > more information. > > > > > > > > > > So, the sequence that I'd like to optimize is mmap(MAP_POPULATE) > > > > > followed > > > > > by mlock(). For example, mmap() takes 1 second to load 4GB data, and > > > > > mlock() > > > > > takes 330ms additionally in order to migrate all the pages into > > > > > inaccessible > > > > > map, IIUC. > > > > > > > > Oh, so the MLOCK part is right, but the inaccessible() part is wrong. > > > > Inaccessible is special weird guest_memfd crap that has all kinds of > > > > side-effects that you don't want. > > > > > > > > Wouldn't you get the same effect by calling mlock2(MLOCK_ONFAULT) and > > > > then calling readahead() for the desired range? > > > > > > Oh, thank you. Let me try. > > > > After checking the code and experiment, I don't think that gives what we > > need. > > That flag skips populate_vma_page_range only, but we need to allocate pages > > in the inaccessible mapping and fill the pages afterwards. > > Then either I don't understand what you're trying to do, or you don't > understand what the inaccessible mapping is for. Is this just for > speeding up mlock() as you suggested earlier, or are you genuinely > trying to do something with the inaccessible mapping?
The latter. I'd like to propose a new read flow with the inaccessible mapping. As-Is: mmap() -> fadvise(fd, POSIX_FADV_WILLNEED) -> mlock() 1. fadvise() proposal mmap() -> fadvise(fd, POSIX_FADV_MLOCK) : all the pages will be loaded into inaccessible page cache directly 2. mlock2() proposal mmap() -> mlock2(MLOCK_ONFAULT) -> madvise(MADV_POPULATE_READ) If you mean #2, I need to find whether we can get the space for madvise, since we have only fd when reading the pages. And, also I need to find a way to handle the folio order directly instead of starging from 0 in madvise() path. Let me think about it. _______________________________________________ Linux-f2fs-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
