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b=EXKS81pjhnX/T3t20HwM0r+G8lZqOaf7LUBFI4WeNo8HO7Dv9KyGrHaNmXneQ778Z dREeqYHE7e/A5Q+YYwlBlEMv0GobGewa87N0nTR3ppXR/wdBGeAjiI6pjGNSvoMDN0 eZ6UoSXLBoe4MqtKJ4Sl/waE+QXU1BcmAB2ZLjoDSlVhukD+jGCRfVjgbQLsrg0Q7G 3k8082FO++Ml3PQ2eE9k8jCQ/sgc7mfHWX1HgRPZFp3B6oAdg/kxrJoZ4WXe7GELHG an6aeydeJMc45Q290ZgCuvu/l80ioKCKwq5n9oHNf2QpIySP7ObpJ94ugAT9Lw7qtT bvUZsyYFN24uA== Message-ID: Date: Mon, 29 Jun 2026 10:00:39 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/6] mm/page_owner: use MIGRATE_REASON_NONE instead of -1 for last_migrate_reason Content-Language: en-US To: Ye Liu , Zi Yan , Andrew Morton Cc: Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260626024550.25677-1-ye.liu@linux.dev> <20260626024550.25677-3-ye.liu@linux.dev> <407fa67f-3212-4c5a-ac8c-7c5d41479cc9@linux.dev> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSNWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBrZXJuZWwub3JnPsLBsAQTAQoAWhYhBKlA1DSZLC6OmRA9UCJPp+fM gqZkBQJqFFy6GxSAAAAAAAQADm1hbnUyLDIuNSsxLjEyLDIsMgIbAwUJGtCBUAULCQgHAwUV CgkICwUWAgMBAAIeBQIXgAAKCRAiT6fnzIKmZJIUEADFx/tREzUImHrEwVHeSvDFmA7tJysI UVrlvrM09E7GIuzphzv7jYmo8n3ANpCczLEVr4G0syYQdTigaZgv3+FQDIIzhKih1IHhu1Ei XHlywNWKnQxxQEUNi5Mwx43wQz5XVw9F1A7gtKBKNtfogO511hAbrzagrYajyQacEJ/+sfhZ 9Da8ltHIXD8pcYaHUfQgEusCgmEd9+KrUwrTbckFKmYq5chuE6yJ4J0EmWknL096jIE6CnzF FRslQ3B1UKDjxVsm1ZHfir5NeWszLkTvGFsddFaWTgh8UycESG6VQzKXjjewXu2pG7YQYRpj QKm1W5X2TkwWkXRBZTmfmbhxIUMh3+zf5wQ463rSmDN/8v81tdqBtAW6rH/kzg1GvkaTHXn0 507yEHFzBksk2viAuIxxr7km8+/KARYLIdGtx30EG8cKzAUZOK6WqxtNCsXUJNrVE8CWrCaD icoNu7Fs1c5hmPHdSTnU48ce67449DdnO4neLSNhRiGlMHJgfJUmgrxu/hcYeOZ3haWmEQ2w uW1Mh01OHi8QZHCEyAbABrPs9GUgccc/4eYXX9hIgxfSkYzn8f+8NuIFPWl/0uTvjgqU29FQ SbzOLxHq9439Ox40G5mS5eZXRGxITYR+6TXvRGI6P/264jvflnr/pDGUttaikU+0W+1uxgKH cmYbEc7ATQRbGTU1AQgAn0H6UrFiWcovkh6EXVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQ La1PQDUi6j00ChlcR66g9/V0sPIcSutacPKfdKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMh FmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCTsTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sf bAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZOrIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq +aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahKtQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4n jQARAQABwsF8BBgBCgAmAhsMFiEEqUDUNJksLo6ZED1QIk+n58yCpmQFAmfIHFQFCRYU6J8A CgkQIk+n58yCpmS2PA//bqN1LfcotmArgElsa+0EGZSQlYgK48pm8WAeTXTngudP9IJ4SuKY HR5RNjHcBeqN+Me0zxRqYzRb8nGanHEkDyf4Im8DQM8d6vbyU+FcPmG4skud4kgS1zMHnlVd SXfSIwKC/hKgdHG8aBV7545Lz9X6Iohea+94wneD0aw/hqF+QWewGZhWJriWAZtvEkzNjQOi 4U9F/trLten/x7bpphDSnDMKJtITbtzATT1Dq7o7VpIUK1nCTQALMuMjKCdi8OdU/+V+R3O4 0PXWvX8qrvqYapVbZ+9KqT74FsuB0Ya9uXwgBF2Q6cRuETZk5vqaqKxzqoQZCO8AOz/58j6O 2RHNy/mZEN+7tJ5Tsq42zVJ4jxsT8b9YplavCMsnBgDeRWhcbYhCyttoL7nYISyWg4kQYZ/P wIV3OuNv2f8iKYsxNsRuClOAF82+gvqOy1/1pprFjy8uo2pkoOrb63aOP3vO5VHnRKgra6dq NcaZ+c6J4H+nEJGi2SkHAUJz5oBzuThvPudLvPA/SK8sKoM01IRxSihev/S/5WLazXB1PGem OCbvzC1IjWJJraxiDJ5IygokapUa2RP7+WBR22skQ3SSl6G107QgWKSyTOGWEaRmV53vxQLV jXuCmzSSasTL60zq5yGrT4/DYQVSNEUiUbG4pYekxJujNeEDkUlky0Y= In-Reply-To: <407fa67f-3212-4c5a-ac8c-7c5d41479cc9@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Stat-Signature: 3da4nixpmtgwjub89tzjaqrkmmx6zz71 X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 5CAFF40018 X-HE-Tag: 1782720043-152371 X-HE-Meta: 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 g3lESAar d2Gntw8SbkdP/F8FWeNC/gK/9lquTJLVBDxNb0a37ecYDCGOqfSWePVRAMArsUkobm/ll/xzeW98F1dqzW74XUEnp5zcDXBXMr2x5b17cw+b7eMWuL/TOxtJVr1Mphwt9NSUY9YU9KcMA2jzfdvnWltgB5wiUX/C/tR8sjPAsSuG5gWwd3NLytwSgMaWtwwaLFl5B3kk/MWWMmrBaOKgZQgO7m2/ziwxjgFF0xrxdM3OYLUL8rTbXiRcYj7OAwTC2/QtNyOpfok+V1u9YErt/DjQp66HkBiQikG0f14b3FwIeNQre9ryzjZAth3PpfIQahURRJlMqUBHYI00= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/29/26 04:20, Ye Liu wrote: > > > 在 2026/6/27 02:45, Zi Yan 写道: >> On Thu Jun 25, 2026 at 10:45 PM EDT, Ye Liu wrote: >>> The last_migrate_reason field uses -1 as a sentinel value to mean "no >>> migration has happened". Replace the four bare -1 occurrences with a >>> local MIGRATE_REASON_NONE define so the intent is explicit and the >>> magic number is eliminated. >>> >>> No functional change. >>> >>> Signed-off-by: Ye Liu >>> --- >>> mm/page_owner.c | 15 +++++++++++---- >>> 1 file changed, 11 insertions(+), 4 deletions(-) >>> >>> diff --git a/mm/page_owner.c b/mm/page_owner.c >>> index 342549891a8d..ebafa9d7ff07 100644 >>> --- a/mm/page_owner.c >>> +++ b/mm/page_owner.c >>> @@ -21,6 +21,13 @@ >>> */ >>> #define PAGE_OWNER_STACK_DEPTH (16) >>> >>> +/* >>> + * Used to indicate that a page has never been migrated, as the valid >>> + * migrate_reason values are non-negative enum members (MR_* in >>> + * include/linux/migrate_mode.h). >> >> Why not change last_migrate_reason to enum migrate_reason and functions >> pass migrate reasons? MR_TYPES probably can be used to indicate no >> migration has happened if we do not want to add MR_NO_MIGRATION. Indeed. I'd just add a proper MR_NEVER option with a comment. >> folio_set_owner_migrate_reason(), >> __folio_set_owner_migrate_reason(), >> move_hugetlb_state(), and >> __update_page_owner_handle() need to update their signatures for this. They should ideally, but do they "need" as part of this series? But I guess it's not a big deal. > Thanks for the review. > > Using MR_TYPES as a sentinel is problematic - it's used kernel-wide as an > array-size marker (migrate_reason_names[MR_TYPES]). Overloading it to also > mean "never migrated" conflates two unrelated semantics. It also has a Well it's just for tracepoint and dumping page owner. Nothing prevents us assigning a value to MR_NEVER that's not -1 (just make MR_NEVER the first or last option of the enum) and a give it a name e.g. "never_migrated" in include/trace/events/migrate.h > subtle out-of-bounds risk: if anyone ever uses the field as an array index > without the guard check, MR_TYPES silently points past the end of the array, > while -1 faults immediately. That wouldn't be a problem either with a proper value. > Adding MR_NONE = -1 to the enum is the right long-term fix, but that needs > proper enum definition changes and cascading signature updates across multiple > headers — better done as a separate series. > The current patch is a minimal improvement: it kills the magic number and > makes intent explicit without touching any header. Minimal fixes are sometimes necessary for actual bugs, for stable backport etc. Nothing prevents us doing it properly here. >> >>> + */ >>> +#define MIGRATE_REASON_NONE (-1) >>> + >>> struct page_owner { >>> unsigned short order; >>> short last_migrate_reason; >>> @@ -339,7 +346,7 @@ noinline void __set_page_owner(struct page *page, unsigned short order, >>> depot_stack_handle_t handle; >>> >>> handle = save_stack(gfp_mask); >>> - __update_page_owner_handle(page, handle, order, gfp_mask, -1, >>> + __update_page_owner_handle(page, handle, order, gfp_mask, MIGRATE_REASON_NONE, >>> ts_nsec, current->pid, current->tgid, >>> current->comm); >>> inc_stack_record_count(handle, gfp_mask, 1 << order); >>> @@ -596,7 +603,7 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn, >>> if (ret >= count) >>> goto err; >>> >>> - if (page_owner->last_migrate_reason != -1) { >>> + if (page_owner->last_migrate_reason != MIGRATE_REASON_NONE) { >>> ret += scnprintf(kbuf + ret, count - ret, >>> "Page has been migrated, last migrate reason: %s\n", >>> migrate_reason_names[page_owner->last_migrate_reason]); >>> @@ -667,7 +674,7 @@ void __dump_page_owner(const struct page *page) >>> stack_depot_print(handle); >>> } >>> >>> - if (page_owner->last_migrate_reason != -1) >>> + if (page_owner->last_migrate_reason != MIGRATE_REASON_NONE) >>> pr_alert("page has been migrated, last migrate reason: %s\n", >>> migrate_reason_names[page_owner->last_migrate_reason]); >>> page_ext_put(page_ext); >>> @@ -826,7 +833,7 @@ static void init_pages_in_zone(struct zone *zone) >>> >>> /* Found early allocated page */ >>> __update_page_owner_handle(page, early_handle, 0, 0, >>> - -1, local_clock(), current->pid, >>> + MIGRATE_REASON_NONE, local_clock(), current->pid, >>> current->tgid, current->comm); >>> count++; >>> ext_put_continue: >> >> >> >> >