On Fri, 14 Aug 2020 10:20:11 +0800 Zhaoyang Huang <huangzhaoyang@xxxxxxxxx> wrote: > On Fri, Aug 14, 2020 at 10:07 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > > > On Fri, Aug 14, 2020 at 02:43:55AM +0100, Matthew Wilcox wrote: > > > On Fri, Aug 14, 2020 at 09:30:11AM +0800, Zhaoyang Huang wrote: > > > > file->f_ra->ra_pages will remain the initialized value since it opend, which may > > > > be NOT equal to bdi->ra_pages as the latter one is updated somehow(etc, > > > > echo xxx > /sys/block/dm/queue/read_ahead_kb).So sync ra->ra_pages to the > > > > updated value when sync read. > > > > > > It still ignores the work done by shrink_readahead_size_eio() > > > and fadvise(POSIX_FADV_SEQUENTIAL). > > > > ... by the way, if you're trying to update one particular file's readahead > > state, you can just call fadvise(POSIX_FADV_NORMAL) on it. > > > > If you want to update every open file's ra_pages by writing to sysfs, > > then just no. We don't do that. > No, What I want to fix is the file within one process's context keeps > using the initialized value when it is opened and not sync with new > value when bdi->ra_pages changes. So you're saying that echo xxx > /sys/block/dm/queue/read_ahead_kb does not affect presently-open files, and you believe that it should do so? I guess that could be a reasonable thing to want - it's reasonable for a user to expect that writing to a global tunable will take immediate global effect. I guess. But as Matthew says, it would help if you were to explain why this is needed. In full detail. What operational problems is the present implementation causing?
