-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 02/18/2015 06:31 PM, Andrew Morton wrote: > On Wed, 11 Feb 2015 23:03:55 +0200 Ebru Akagunduz > <ebru.akagunduz@xxxxxxxxx> wrote: > >> This patch improves THP collapse rates, by allowing zero pages. >> >> Currently THP can collapse 4kB pages into a THP when there are up >> to khugepaged_max_ptes_none pte_none ptes in a 2MB range. This >> patch counts pte none and mapped zero pages with the same >> variable. > > So if I'm understanding this correctly, with the default value of > khugepaged_max_ptes_none (HPAGE_PMD_NR-1), if an application > creates a 2MB area which contains 511 mappings of the zero page and > one real page, the kernel will proceed to turn that area into a > real, physical huge page. So it consumes 2MB of memory which would > not have previously been allocated? This is equivalent to an application doing a write fault to a 2MB area that was previously untouched, going into do_huge_pmd_anonymous_page() and receiving a 2MB page. > If so, this might be rather undesirable behaviour in some > situations (and ditto the current behaviour for pte_none ptes)? > > This can be tuned by adjusting khugepaged_max_ptes_none, The example of directly going into do_huge_pmd_anonymous_page() is not influenced by the tunable. It may indeed be undesirable in some situations, but I am not sure how to detect those... - -- All rights reversed -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQEcBAEBAgAGBQJU5SlsAAoJEM553pKExN6D8DYH/0TQPr38R3lYqxTllOVPIUus +UrgXveOeoMiMbN3e5r9tIJkw+2yUJFZ8hkYx+aFsTD5zNz7xwf9Qz8IdJpcZ3sc PkvOnnZNk/ZzixWrBhWFPsKRN2pi5wXMpfNM2jTs9W4EeyfkV3RYbGxZy/OO1LB5 CwDzteCTb81y1FYxC4vNxLnML417ZjIMq7ICdj6lKW2KC5+TdCIPTOrKCy+2fWBo 4qhqho4RFKHLCxpnryUMzZDXca4vmcgGWwUm5xLF6SnJWWFEiPBLixJiRV3xe0iw rbuGhcIXo/q16oO4QOIl+hSVJr8vE+Y8xRbIJFmWXCmuQHQpg5ZspVZ+9Z/3UaI= =Qf1D -----END PGP SIGNATURE----- -- 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>