On Sat, 22 Oct 2016, Kirill A. Shutemov wrote: > > Huge pages are detrimental for small file: they causes noticible > overhead on both allocation performance and memory footprint. > > This patch aimed to address this issue by avoiding huge pages until file > grown to size of huge page. This would cover most of the cases where huge > pages causes regressions in performance. > > Couple notes: > > - if shmem_enabled is set to 'force', the limit is ignored. We still > want to generate as many pages as possible for functional testing. > > - the limit doesn't affect khugepaged behaviour: it still can collapse > pages based on its settings; > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Sorry, but NAK. I was expecting a patch to tune within_size behaviour. > --- > Documentation/vm/transhuge.txt | 3 +++ > mm/shmem.c | 5 +++++ > 2 files changed, 8 insertions(+) > > diff --git a/Documentation/vm/transhuge.txt b/Documentation/vm/transhuge.txt > index 2ec6adb5a4ce..d1889c7c8c46 100644 > --- a/Documentation/vm/transhuge.txt > +++ b/Documentation/vm/transhuge.txt > @@ -238,6 +238,9 @@ values: > - "force": > Force the huge option on for all - very useful for testing; > > +To avoid overhead for small files, we don't allocate huge pages for a file > +until it grows to size of huge pages. > + > == Need of application restart == > > The transparent_hugepage/enabled values and tmpfs mount option only affect > diff --git a/mm/shmem.c b/mm/shmem.c > index ad7813d73ea7..49618d2d6330 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -1692,6 +1692,11 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index, > goto alloc_huge; > /* TODO: implement fadvise() hints */ > goto alloc_nohuge; > + case SHMEM_HUGE_ALWAYS: > + i_size = i_size_read(inode); > + if (index < HPAGE_PMD_NR && i_size < HPAGE_PMD_SIZE) > + goto alloc_nohuge; > + break; > } > > alloc_huge: So (eliding the SHMEM_HUGE_ADVISE case in between) you now have: case SHMEM_HUGE_WITHIN_SIZE: off = round_up(index, HPAGE_PMD_NR); i_size = round_up(i_size_read(inode), PAGE_SIZE); if (i_size >= HPAGE_PMD_SIZE && i_size >> PAGE_SHIFT >= off) goto alloc_huge; goto alloc_nohuge; case SHMEM_HUGE_ALWAYS: i_size = i_size_read(inode); if (index < HPAGE_PMD_NR && i_size < HPAGE_PMD_SIZE) goto alloc_nohuge; goto alloc_huge; I'll concede that those two conditions are not the same; but again you're messing with huge=always to make it, not always, but conditional on size. Please, keep huge=always as is: if I copy a 4MiB file into a huge tmpfs, I got ShmemHugePages 4096 kB before, which is what I wanted. Whereas with this change I get only 2048 kB, just like with huge=within_size. Treating the first extent differently is a hack, and does not respect that this is a filesystem, on which size is likely to increase. By all means refine the condition for huge=within_size, and by all means warn in transhuge.txt that huge=always may tend to waste valuable huge pages if the filesystem is used for small files without good reason (but maybe the implementation needs to reclaim those more effectively). Hugh -- 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>