From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E06983264D7 for ; Tue, 9 Jun 2026 12:52:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781009543; cv=none; b=HiT1bZHtxc8bGsK8XmvVftUwMH7+BT+m0gd/kyKP6EUNMNGDmYsfJSoJ2Dp9J1rwEAjZzzmk9chyOTsYVUikbGM6TBejwhJ9040gLlIZNMQF9Fufp+ZYFFGi/bi8urM6PFp2o/9ypzV5qqZKeP1zOKUxjNIJkXSncVacsrvAIQE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781009543; c=relaxed/simple; bh=BjbzfGT9jgeR6AZaJA+9u+LIxU9ztl30CqrlVtOL/Os=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=p7Kh0EDlydE+FK+bPDXfLJeGYuvg2cZyZgz1vsQM05SByKoSuc9Odr7zvYohWYsce7sGXjIlYEaR2WILByGzUcMrL3j5UiEjxTOhGQy/id9ot2qDpidjjUG65iGNak7KquxZTwSttsuzleY1xEqISebfMmNEKcgag/pkIckn5T0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=gMsLiJ/k; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="gMsLiJ/k" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 61E1A1F00893; Tue, 9 Jun 2026 12:52:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781009542; bh=6RVksM1q/xCzaj5QI2KqOkAZj28JqLKLzQFq6yryIo4=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=gMsLiJ/kd4lFpp0rUts/FQ32exqVF+EjEbMhMwmzetICiVvEWYclp910lfp2WZR2a wpZJxiFq94Qxa6otRthSQVe/XirLEXN+bi2tek4xxWokxIhvt7yN9SiPYoWCv21pOL N9eG3lcDurR5E+WXDoao2/Ca6NFb1IcLADYTFgSr1s6DTJcLIVSjgmCm50InLQ6bMI WPgTGrpIPE92wCnJb0frum0xr3FCUiIF9EsjNJxfNji9rB273wouFm1GLaY2YNcbaL ZJ7HIpzG4xrt6TbjAhh73IdJUmhiwnYwPGk5nLG8ABMdHAfJyjtIlSsEk74UBj/KIg qxS8qP2qe616Q== Message-ID: Date: Tue, 9 Jun 2026 14:52:18 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 0/8] mm/slab: enable runtime sheaves tuning Content-Language: en-US To: Harry Yoo , Pedro Falcato Cc: Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Suren Baghdasaryan , "Liam R. Howlett" References: <20260516-sheaves-tuning-v1-0-221aa3e1d829@kernel.org> <682945f5-2d00-4bc8-8e23-59189b4472c6@kernel.org> 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: <682945f5-2d00-4bc8-8e23-59189b4472c6@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/20/26 06:35, Harry Yoo wrote: > >>> ========== >>> >>> 1. Allocations and frees can happen concurrently at any point between >>> these steps, and we cannot introduce heavyweight synchronization >>> mechanisms on the fastpath. >>> >>> 2. Currently, cache_has_sheaves() checks whether a cache has sheaves. >>> This works now because sheaves cannot be enabled or disabled once >>> the cache is created. >>> >>> The question "Does this cache has sheaves?" should be split into >>> "Does this cache support sheaves?" and "Does this CPU actually has >>> sheaves enabled right now?". >>> >>> 3. Once the sheaf capacity update is complete, no sheaf with stale >>> capacity must remain. >> >> Why? I don't see a huge problem with having multiple sheaves with different >> capacities, as long as you adequately, opportunistically kill the sheaves >> if they don't have the desired size (say, once a sheaf is fully empty). > > Haha, you got me. > > Right, enforcing a single capacity at any given point introduced so much > complexity that I started wondering myself about whether this is really > essential. > > My main concern was that the performance characteristics would become > too unpredictable, but actually, users can avoid that by disabling > sheaves, shrinking it, and re-enabling it. So that's not an enough > justification. My concern would have been that we would need to track capacity per sheaf if we allowed sheaves with different capacities to coexist. But patch 3 here already does that, so it seems it's necessary anyway... > When I first started, I was quite cautious and obsessed with the > invariant because many parts of the current implementation assume "a > kmem_cache has only a single capacity, and it doesn't change", but > that's also addressed by this patchset. So that's not a big issue either. > > I agree that it is worth trying to allow sheaves of different capacities > and hopefully that would be less intrusive. Let's see. > > Thank you, Pedro. >