On Mon 25-07-16 13:47:32, Andrew Morton wrote: > On Mon, 25 Jul 2016 10:39:25 -0400 Kyle Walker <kwalker@xxxxxxxxxx> wrote: > > > Java workloads using the MappedByteBuffer library result in the fadvise() > > and madvise() syscalls being used extensively. Following recent readahead > > limiting alterations, such as 600e19af ("mm: use only per-device readahead > > limit") and 6d2be915 ("mm/readahead.c: fix readahead failure for > > memoryless NUMA nodes and limit readahead pages"), application performance > > suffers in instances where small readahead is configured. > > Can this suffering be quantified please? > > > By moving this limit outside of the syscall codepaths, the syscalls are > > able to advise an inordinately large amount of readahead when desired. > > With a cap being imposed based on the half of NR_INACTIVE_FILE and > > NR_FREE_PAGES. In essence, allowing performance tuning efforts to define a > > small readahead limit, but then benefiting from large sequential readahead > > values selectively. > > > > ... > > > > --- a/mm/readahead.c > > +++ b/mm/readahead.c > > @@ -211,7 +211,9 @@ int force_page_cache_readahead(struct address_space *mapping, struct file *filp, > > if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages)) > > return -EINVAL; > > > > - nr_to_read = min(nr_to_read, inode_to_bdi(mapping->host)->ra_pages); > > + nr_to_read = min(nr_to_read, (global_page_state(NR_INACTIVE_FILE) + > > + (global_page_state(NR_FREE_PAGES)) / 2)); > > + > > while (nr_to_read) { > > int err; > > > > @@ -484,6 +486,7 @@ void page_cache_sync_readahead(struct address_space *mapping, > > > > /* be dumb */ > > if (filp && (filp->f_mode & FMODE_RANDOM)) { > > + req_size = min(req_size, inode_to_bdi(mapping->host)->ra_pages); > > force_page_cache_readahead(mapping, filp, offset, req_size); > > return; > > } > > Linus probably has opinions ;) Just for the reference a similar patch has been discussed already [1] or from a different angle [2] [1] http://lkml.kernel.org/r/1440087598-27185-1-git-send-email-klamm@xxxxxxxxxxxxxx [2] http://lkml.kernel.org/r/1456277927-12044-1-git-send-email-hannes@xxxxxxxxxxx -- Michal Hocko SUSE Labs -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>