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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spamd-Result: default: False [-3.01 / 50.00]; BAYES_HAM(-3.00)[99.99%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FREEMAIL_TO(0.00)[gmail.com,linux-foundation.org]; FUZZY_RATELIMITED(0.00)[rspamd.com]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; ARC_NA(0.00)[]; RCPT_COUNT_TWELVE(0.00)[12]; MIME_TRACE(0.00)[0:+]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; RCVD_TLS_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; TAGGED_RCPT(0.00)[]; DKIM_TRACE(0.00)[suse.cz:+]; DBL_BLOCKED_OPENRESOLVER(0.00)[thingy.jp:email,suse.cz:dkim,suse.cz:mid,roeck-us.net:email] X-Rspamd-Action: no action X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Spam-Level: X-Rspamd-Queue-Id: 225AB5BCEC X-Spam-Flag: NO X-Spam-Score: -3.01 On 12/17/25 12:12, Vlastimil Babka wrote: > On 12/17/25 07:05, Joshua Hahn wrote: >> Commit 2783088ef24e ("mm/page_alloc: prevent reporting pcp->batch = 0") >> moved the error handling (0-handling) of zone_batchsize from its >> callers to inside the function. However, the commit left out the error >> handling for the NOMMU case, leading to deadlocks on NOMMU systems. >> >> Since in the NOMMU case the reported-to-user batchsize should still be 0, > > Should it? The value is effectively set to 1 despite what zone_batchsize() > returns, because of that adjustment this patch reinstates. Also does anyone > care, really? > >> we would only like the error handling to exist in the callsites that >> set the internal value for the zone (i.e. zone_set_pageset_high_and_batch). >> >> Restore max(1, zone_batchsize(zone)) to the callsite to prevent errors >> on NOMMU systems. > > I would rather make zone_batchsize() for !CONFIG_MMU return 1 instead of 0. Ah looks like you considered it too, initially: https://lore.kernel.org/all/20251211225947.822866-1-joshua.hahnjy@gmail.com/ It makes more sense to me than doing effectively two fixups in the MMU case. >> Fixes: 2783088ef24e ("mm/page_alloc: prevent reporting pcp->batch = 0") >> Reported-by: Daniel Palmer >> Closes: https://lore.kernel.org/linux-mm/CAFr9PX=_HaM3_xPtTiBn5Gw5-0xcRpawpJ02NStfdr0khF2k7g@mail.gmail.com/ >> Reported-by: Guenter Roeck >> Closes: https://lore.kernel.org/all/42143500-c380-41fe-815c-696c17241506@roeck-us.net/ >> Signed-off-by: Joshua Hahn >> --- >> mm/page_alloc.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index 822e05f1a964..10c1297fd3ea 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -6045,7 +6045,7 @@ static void zone_set_pageset_high_and_batch(struct zone *zone, int cpu_online) >> { >> int new_high_min, new_high_max, new_batch; >> >> - new_batch = zone_batchsize(zone); >> + new_batch = max(1, zone_batchsize(zone)); >> if (percpu_pagelist_high_fraction) { >> new_high_min = zone_highsize(zone, new_batch, cpu_online, >> percpu_pagelist_high_fraction); >> >> base-commit: 40fbbd64bba6c6e7a72885d2f59b6a3be9991eeb >