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Thu, 8 Dec 2022 17:55:00 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id vKFENvQkkmP8TAAAMHmgww (envelope-from ); Thu, 08 Dec 2022 17:55:00 +0000 Message-ID: Date: Thu, 8 Dec 2022 18:55:00 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.1 Subject: Re: [PATCH 4/6] mm/page_alloc: Explicitly define what alloc flags deplete min reserves Content-Language: en-US To: Mel Gorman , Linux-MM Cc: Andrew Morton , Michal Hocko , NeilBrown , Thierry Reding , Matthew Wilcox , LKML References: <20221129151701.23261-1-mgorman@techsingularity.net> <20221129151701.23261-5-mgorman@techsingularity.net> From: Vlastimil Babka In-Reply-To: <20221129151701.23261-5-mgorman@techsingularity.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: bzasq1iz5wpxu3o4ch4yq6ni6njasfat X-Rspam-User: X-Rspamd-Queue-Id: D6DB320014 X-Rspamd-Server: rspam06 X-HE-Tag: 1670522102-785340 X-HE-Meta: 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 pM6v79sb x/1DDqr1tEf1ph8hssnvnByRSA66gItB9hVfAh5e1v1hzSRBJznFleGvKzQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 11/29/22 16:16, Mel Gorman wrote: > As there are more ALLOC_ flags that affect reserves, define what flags > affect reserves and clarify the effect of each flag. Seems to me this does more than a clarification, but also some functional tweaks, so it could be helpful if those were spelled out in the changelog. > Signed-off-by: Mel Gorman > --- > mm/internal.h | 3 +++ > mm/page_alloc.c | 36 +++++++++++++++++++++++------------- > 2 files changed, 26 insertions(+), 13 deletions(-) > > diff --git a/mm/internal.h b/mm/internal.h > index 9a9d9b5ee87f..370500718732 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -757,6 +757,9 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone, > #define ALLOC_HIGHATOMIC 0x200 /* Allows access to MIGRATE_HIGHATOMIC */ > #define ALLOC_KSWAPD 0x800 /* allow waking of kswapd, __GFP_KSWAPD_RECLAIM set */ > > +/* Flags that allow allocations below the min watermark. */ > +#define ALLOC_RESERVES (ALLOC_HARDER|ALLOC_MIN_RESERVE|ALLOC_HIGHATOMIC|ALLOC_OOM) > + > enum ttu_flags; > struct tlbflush_unmap_batch; > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index e2b65767dda0..85a87d0ac57a 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3944,15 +3944,14 @@ ALLOW_ERROR_INJECTION(should_fail_alloc_page, TRUE); > static inline long __zone_watermark_unusable_free(struct zone *z, > unsigned int order, unsigned int alloc_flags) > { > - const bool alloc_harder = (alloc_flags & (ALLOC_HARDER|ALLOC_OOM)); > long unusable_free = (1 << order) - 1; > > /* > - * If the caller does not have rights to ALLOC_HARDER then subtract > - * the high-atomic reserves. This will over-estimate the size of the > - * atomic reserve but it avoids a search. > + * If the caller does not have rights to reserves below the min > + * watermark then subtract the high-atomic reserves. This will > + * over-estimate the size of the atomic reserve but it avoids a search. > */ > - if (likely(!alloc_harder)) > + if (likely(!(alloc_flags & ALLOC_RESERVES))) > unusable_free += z->nr_reserved_highatomic; > > #ifdef CONFIG_CMA > @@ -3976,25 +3975,36 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark, > { > long min = mark; > int o; > - const bool alloc_harder = (alloc_flags & (ALLOC_HARDER|ALLOC_OOM)); > > /* free_pages may go negative - that's OK */ > free_pages -= __zone_watermark_unusable_free(z, order, alloc_flags); > > - if (alloc_flags & ALLOC_MIN_RESERVE) > - min -= min / 2; > + if (alloc_flags & ALLOC_RESERVES) { Do we want to keep this unlikely() as alloc_harder did before? > + /* > + * __GFP_HIGH allows access to 50% of the min reserve as well > + * as OOM. > + */ > + if (alloc_flags & ALLOC_MIN_RESERVE) > + min -= min / 2; > > - if (unlikely(alloc_harder)) { > /* > - * OOM victims can try even harder than normal ALLOC_HARDER > + * Non-blocking allocations can access some of the reserve > + * with more access if also __GFP_HIGH. The reasoning is that > + * a non-blocking caller may incur a more severe penalty > + * if it cannot get memory quickly, particularly if it's > + * also __GFP_HIGH. > + */ > + if (alloc_flags & (ALLOC_HARDER|ALLOC_HIGHATOMIC)) > + min -= min / 4; For example this seems to change the allowed dip to reserves for ALLOC_HIGHATOMIC. > + > + /* > + * OOM victims can try even harder than the normal reserve > * users on the grounds that it's definitely going to be in > * the exit path shortly and free memory. Any allocation it > * makes during the free path will be small and short-lived. > */ > if (alloc_flags & ALLOC_OOM) > min -= min / 2; > - else > - min -= min / 4; > } (noted that this patch doesn't seem to change the concern I raised in previous patch) > /* > @@ -5293,7 +5303,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > * could deplete whole memory reserves which would just make > * the situation worse > */ > - page = __alloc_pages_cpuset_fallback(gfp_mask, order, ALLOC_HARDER, ac); > + page = __alloc_pages_cpuset_fallback(gfp_mask, order, ALLOC_MIN_RESERVE|ALLOC_HARDER, ac); And this AFAICS seems to give __GFP_NOFAIL 3/4 of min reserves instead of 1/4, which seems like a significant change (but hopefully ok) so worth noting at least. > if (page) > goto got_pg; >