-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 03/12/2015 03:30 PM, Michal Hocko wrote: > On Thu 12-03-15 11:22:56, Eric B Munson wrote: >> Currently, pages which are marked as unevictable are protected >> from compaction, but not from other types of migration. The >> mlock desctription does not promise that all page faults will be >> avoided, only major ones so this protection is not necessary. >> This extra protection can cause problems for applications that >> are using mlock to avoid swapping pages out, but require order > >> 0 allocations to continue to succeed in a fragmented environment. >> This patch adds a sysctl entry that will be used to allow root to >> enable compaction of unevictable pages. > > It would be appropriate to add a justification for the sysctl, > because it is not obvious from the above description. mlock > preventing from the swapout is not sufficient to justify it. It is > the real time extension mentioned by Peter in the previous version > which makes it worth a new user visible knob. > > I would also argue that the knob should be enabled by default > because the real time extension requires an additional changes > anyway (rt-kernel at least) while general usage doesn't need such a > strong requirement.
Thanks for the review, I will incorporate your suggestions into a V5. I agree that many users will want to set this to 1, but keeping the default to 0 maintains the behavior of the kernel today. I'd like to have the real time folks say that they are okay with a default of 1 before I make that change. > > You also should provide a knob description to > Documentation/sysctl/vm.txt Will do. > >> To illustrate this problem I wrote a quick test program that >> mmaps a large number of 1MB files filled with random data. These >> maps are created locked and read only. Then every other mmap is >> unmapped and I attempt to allocate huge pages to the static huge >> page pool. When the compact_unevictable sysctl is 0, I cannot >> allocate hugepages after fragmenting memory. When the value is >> set to 1, allocations succeed. >> >> Signed-off-by: Eric B Munson <[email protected]> Cc: Vlastimil >> Babka <[email protected]> Cc: Thomas Gleixner <[email protected]> >> Cc: Christoph Lameter <[email protected]> Cc: Peter Zijlstra >> <[email protected]> Cc: Mel Gorman <[email protected]> Cc: David >> Rientjes <[email protected]> Cc: Rik van Riel >> <[email protected]> Cc: [email protected] Cc: >> [email protected] > > After the above things are fixed Acked-by: Michal Hocko > <[email protected]> > > One minor suggestion below > >> diff --git a/kernel/sysctl.c b/kernel/sysctl.c index >> 88ea2d6..cc1a678 100644 --- a/kernel/sysctl.c +++ >> b/kernel/sysctl.c @@ -1313,6 +1313,13 @@ static struct ctl_table >> vm_table[] = { .extra1 = &min_extfrag_threshold, .extra2 >> = >> &max_extfrag_threshold, }, + { + .procname = >> "compact_unevictable", + .data = >> &sysctl_compact_unevictable, + >> .maxlen = sizeof(int), + .mode = 0644, >> + .proc_handler = >> proc_dointvec, > > You can use .extra1 = &zero and .extra2 = &one to reduce the value > space. > -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) iQIcBAEBAgAGBQJVAezjAAoJELbVsDOpoOa9MHwP/j4nvm3dFm00qjOX4RKxsalz cjhQxuozKnRU9H+OPS3dXXoqDGdpLaLu6CsUsu8FGiJj3zLgUNxea+quJSnSmYVz 8fO5VqhgA3alu7R7zSF3MtOjLzyOoP5/+jDNiNUDLL8sUzg/3hKXLUgBO9R1VU4Q yD0Yuhw5veNLOvF57xhMCk/quCydIvZV9kAJyTr+fgoY4b8wLyp+QAcqi2lGMCBj 4W9lXtO1abG+gu/m5zAhXLX7MS+ZRQtA070G+kmkY7Z95DtKePGitNjLN7+X9EI6 F1073D+GtiEOJhC+xNOc6Xzwpfl4vRghg4jj6aTkSSrb+sY5/byuKg06p8rMRfef pJrqjprbBNqiAP95z7X9H6FWty31kx6ZVXtM8CA9/XDqabJGgGs0qmDwPVf264+M 8ySZy5wPRE85yNUKElpvDnx7+t1gka8vDy3bVO+zPsJV3ZqSwhgAiYTTL6u2f/Qe QwMXWgu4PaAeq0Wltrd/OtA6Fu9H9A91rkk8t69ctPkTjZYCgN0UDGzaa0WpH9SB H2mz2B3+AE2sdpuoBoVQ62SU4/7PiBIT/ILRuzgQnnNELZFStjstRZPrnVSAYRKI E5ArRQHfMwbortIiz9KH8SoibTyS0QZiXuKua6LXPwGTnvYqsSN8Jz1XoytV3I5G MRhLUI7k4dgaVHPTVUYb =qBj6 -----END PGP SIGNATURE----- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
