From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793672154; b=5lDnw53ij+uxSop1//oJ2a0RyR3S1H8ZRkSxerfMeGfm5W19cuXF3WeQ8wZDxIV8Bhvo mQZsNr1a7SV/ClsvnBI4Iwa0sItVUeUeoiEPjcQv23923t01pUxMhbpyn4+zPdceUqlSW zLHYRfz1rioGmPVDiQKdYXivkxBT2q8YX52eq6OifvC5PWzNJkX+q8mX+L3y/GoRXpg4W mxz39HDeTYteFf09w41X+g1815Mvojwv5+apmAQFAL0mmsZXocBNCdXwWeydWk9xMGxUN Eg38wgnq94y5pJU1+S5fFMpYPO2Sw2pQ35ixhGviJ21gnbHGqK1UJQBa4DtmYe76Y+w== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793672154; h=Received:DKIM-Signature:Date:To:From:Subject:Message-Id; bh=8zc82ypHzo61GO4HphwSBWFVY9RadgorQVLqlpKErQY=; b=aCH6YDXvhnm1axVLjYPxNQ/8UoriI1sbnWLoyZeUOD66pQl85LzpkMMt+96f8lh/qnja YcWn7pIusIsYc6GguLCmqRn41w9roB4Pb3MpohR/ZrKRn8Lr+kPi7NfCc4/OfJ8qPeDe7 roiDCWQ8XgcpO92JF/NLsyjR3qviXLdfnGqJtu7n4p+1nKEQVF51grrERcTjvLoLob41M UQEXjyhKrqDBz3aDhKrduepWW1nwkEZHGP1qy8RvSXKzXTp/CHivQcMmknEt/SdrR71lo ujSv4vbW4PEf+NhCuxRse8rL29538k1WLv8O180c0avdPOhywPyzNZB8Aep2bLv+WZA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linux-foundation.org header.i=@linux-foundation.org header.a=rsa-sha256 header.s=korg header.b=TfVWb82H; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7636A606A333; Tue, 3 Nov 2026 02:15:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux-foundation.org header.i=@linux-foundation.org header.a=rsa-sha256 header.s=korg header.b=TfVWb82H Received: by smtp.kernel.org (Postfix) with ESMTPSA id 360061F0093A; Tue, 3 Nov 2026 02:15:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1793672154; bh=8zc82ypHzo61GO4HphwSBWFVY9RadgorQVLqlpKErQY=; h=Date:To:From:Subject; b=TfVWb82H2IMiZvSnzVkT4SQlTKnIpnQY7PHvyQj0GdwWSfl/0FhN7VSH5HdsChwa7 gKComxhAffPO6cAcEvt8wQu9/ukburB9UuILTsLsZeFWBwgRC1tFxokWJm5M9BIWds HVAe2ww/hp9NNFeuoqa3q54fe6OiM9yGnqQSMzCs= Date: Mon, 02 Nov 2026 18:15:53 -0800 To: mm-commits@vger.kernel.org,ziy@nvidia.com,willy@infradead.org, vbabka@kernel.org,surenb@google.com,stable@vger.kernel.org,mhocko@suse.com, mgorman@techsingularity.net,matt@readmodwrite.com,hch@lst.de, dipiets@amazon.it,dgc@kernel.org,brendan.jackman@linux.dev, balbirs@nvidia.com,hannes@cmpxchg.org,akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-hotfixes-stable] mm-page_alloc-remove-alloc_non_block-from-alloc_reserves.patch removed from -mm tree Message-Id: <20261103021554.360061F0093A@smtp.kernel.org> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list The quilt patch titled Subject: mm: page_alloc: remove ALLOC_NON_BLOCK from ALLOC_RESERVES has been removed from the -mm tree. Its filename was mm-page_alloc-remove-alloc_non_block-from-alloc_reserves.patch This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Johannes Weiner Subject: mm: page_alloc: remove ALLOC_NON_BLOCK from ALLOC_RESERVES Date: Wed, 28 Oct 2026 13:15:54 -0400 1ebbb21811b7 ("mm/page_alloc: explicitly define how __GFP_HIGH non-blocking allocations accesses reserves") stopped handing out reserve access for ALLOC_NON_BLOCK on its own: the extra 25% below the min watermark is now only granted on top of ALLOC_MIN_RESERVE. But the flag was left in ALLOC_RESERVES, which produces something odd: With the ALLOC_RESERVES match, __zone_watermark_unusable_free() doesn't subtract the free highatomic pages for them. So in the slowpath, they get to consume regular blocks below the min watermark by the number of free highatomic pages. The highatomic reserve is capped at 1% of the zone, which on any decently sized machine is a multiple of the min watermark: GFP_NOWAIT can drain regular memory to zero. The user-visible result is brutal hiccups during bursts of GFP_NOWAIT allocations under memory pressure. This was found in review and reproduced with a synthetic burst, not observed in production, but the sequence of events is a realistic one: On a 32G box with an anonymous working set, swap, and a filled 290M highatomic reserve, a GFP_NOWAIT burst drove regular free memory in the 28G Normal zone (min=60M) to 28M, 0.8M and 0.6M in three runs. Swapout failed to allocate its swap table, reclaim scanned 13M pages to reclaim 200k, page faults stalled for tens to hundreds of milliseconds. The machine survives it, but not by design: direct reclaimers eventually fail and start unreserving highatomic blocks, until the allocation succeeds or the reserve is gone and the OOM killer runs. That reserve exists for high-order atomic allocations; here it is destroyed to bail out a GFP_NOWAIT consumer that was never entitled to the memory. Remove ALLOC_NON_BLOCK from ALLOC_RESERVES. With that, the GFP_NOWAIT burst is stopped short at the min watermark. No direct reclaim, no stalls, no failed allocations, and the highatomic reserve stays intact for the requests it exists for. __zone_watermark_ok() is unaffected, since everything it keys on ALLOC_NON_BLOCK is already nested under ALLOC_MIN_RESERVE. Update the flag comments accordingly: ALLOC_NON_BLOCK just means the caller can't block; the reserve math belongs with ALLOC_MIN_RESERVE. GFP_ATOMIC order-0 requests have a milder version of the same problem. Through ALLOC_MIN_RESERVE they also count the free highatomic pages in their watermark check, but rmqueue_buddy() serves them regular pages first and only falls back to the reserve once those are gone. They can still push regular free memory to 37.5% of min minus the free highatomic pages before the reserve is touched. Unlike GFP_NOWAIT they are entitled to the reserve, so this needs the watermark check and the freelist order reworked together, and is left to a separate patch. Link: https://lore.kernel.org/20261028171719.2043421-3-hannes@cmpxchg.org Fixes: 1ebbb21811b7 ("mm/page_alloc: explicitly define how __GFP_HIGH non-blocking allocations accesses reserves") Signed-off-by: Johannes Weiner Signed-off-by: Andrew Morton Acked-by: Balbir Singh Reviewed-by: Vlastimil Babka (SUSE) Cc: Matthew Wilcox (Oracle) Cc: Salvatore Dipietro Cc: Christoph Hellwig Cc: Dave Chinner Cc: Matt Fleming Cc: Mel Gorman Cc: Michal Hocko Cc: Suren Baghdasaryan Cc: Brendan Jackman Cc: Zi Yan Cc: --- mm/page_alloc.h | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) --- a/mm/page_alloc.h~mm-page_alloc-remove-alloc_non_block-from-alloc_reserves +++ a/mm/page_alloc.h @@ -32,12 +32,11 @@ #define ALLOC_OOM ALLOC_NO_WATERMARKS #endif -#define ALLOC_NON_BLOCK 0x10 /* Caller cannot block. Allow access - * to 25% of the min watermark or - * 62.5% if __GFP_HIGH is set. - */ +#define ALLOC_NON_BLOCK 0x10 /* Caller cannot block. */ #define ALLOC_MIN_RESERVE 0x20 /* __GFP_HIGH set. Allow access to 50% - * of the min watermark. + * of the min watermark, or 62.5% if + * the caller cannot block either + * (ALLOC_NON_BLOCK). */ #define ALLOC_CPUSET 0x40 /* check for correct cpuset */ #define ALLOC_CMA 0x80 /* allow allocations from CMA areas */ @@ -58,7 +57,7 @@ #define ALLOC_NO_CODETAG 0x1000 /* Flags that allow allocations below the min watermark. */ -#define ALLOC_RESERVES (ALLOC_NON_BLOCK|ALLOC_MIN_RESERVE|ALLOC_HIGHATOMIC|ALLOC_OOM) +#define ALLOC_RESERVES (ALLOC_MIN_RESERVE|ALLOC_HIGHATOMIC|ALLOC_OOM) /* Flags that mean GFP_ATOMIC */ #define ALLOC_MASK_ATOMIC (ALLOC_NON_BLOCK|ALLOC_MIN_RESERVE) _ Patches currently in -mm which might be from hannes@cmpxchg.org are