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([2600:1700:e321:62f0:da43:aeff:fecc:bfd5]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-b0db12743afsm4340690a12.16.2025.04.20.10.42.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 20 Apr 2025 10:42:57 -0700 (PDT) Sender: Guenter Roeck Message-ID: Date: Sun, 20 Apr 2025 10:42:56 -0700 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] xfs: add tunable threshold parameter for triggering zone GC To: Carlos Maiolino Cc: Hans Holmberg , Dave Chinner , "Darrick J . Wong" , hch , "linux-xfs@vger.kernel.org" , "linux-kernel@vger.kernel.org" References: <20250325091007.24070-1-hans.holmberg@wdc.com> <476cf4b6-e3e6-4a64-a400-cc1f05ea44cc@roeck-us.net> Content-Language: en-US From: Guenter Roeck Autocrypt: addr=linux@roeck-us.net; keydata= xsFNBE6H1WcBEACu6jIcw5kZ5dGeJ7E7B2uweQR/4FGxH10/H1O1+ApmcQ9i87XdZQiB9cpN RYHA7RCEK2dh6dDccykQk3bC90xXMPg+O3R+C/SkwcnUak1UZaeK/SwQbq/t0tkMzYDRxfJ7 nyFiKxUehbNF3r9qlJgPqONwX5vJy4/GvDHdddSCxV41P/ejsZ8PykxyJs98UWhF54tGRWFl 7i1xvaDB9lN5WTLRKSO7wICuLiSz5WZHXMkyF4d+/O5ll7yz/o/JxK5vO/sduYDIlFTvBZDh gzaEtNf5tQjsjG4io8E0Yq0ViobLkS2RTNZT8ICq/Jmvl0SpbHRvYwa2DhNsK0YjHFQBB0FX IdhdUEzNefcNcYvqigJpdICoP2e4yJSyflHFO4dr0OrdnGLe1Zi/8Xo/2+M1dSSEt196rXaC kwu2KgIgmkRBb3cp2vIBBIIowU8W3qC1+w+RdMUrZxKGWJ3juwcgveJlzMpMZNyM1jobSXZ0 VHGMNJ3MwXlrEFPXaYJgibcg6brM6wGfX/LBvc/haWw4yO24lT5eitm4UBdIy9pKkKmHHh7s jfZJkB5fWKVdoCv/omy6UyH6ykLOPFugl+hVL2Prf8xrXuZe1CMS7ID9Lc8FaL1ROIN/W8Vk BIsJMaWOhks//7d92Uf3EArDlDShwR2+D+AMon8NULuLBHiEUQARAQABzTJHdWVudGVyIFJv ZWNrIChMaW51eCBhY2NvdW50KSA8bGludXhAcm9lY2stdXMubmV0PsLBgQQTAQIAKwIbAwYL CQgHAwIGFQgCCQoLBBYCAwECHgECF4ACGQEFAlVcphcFCRmg06EACgkQyx8mb86fmYFg0RAA nzXJzuPkLJaOmSIzPAqqnutACchT/meCOgMEpS5oLf6xn5ySZkl23OxuhpMZTVX+49c9pvBx hpvl5bCWFu5qC1jC2eWRYU+aZZE4sxMaAGeWenQJsiG9lP8wkfCJP3ockNu0ZXXAXwIbY1O1 c+l11zQkZw89zNgWgKobKzrDMBFOYtAh0pAInZ9TSn7oA4Ctejouo5wUugmk8MrDtUVXmEA9 7f9fgKYSwl/H7dfKKsS1bDOpyJlqhEAH94BHJdK/b1tzwJCFAXFhMlmlbYEk8kWjcxQgDWMu GAthQzSuAyhqyZwFcOlMCNbAcTSQawSo3B9yM9mHJne5RrAbVz4TWLnEaX8gA5xK3uCNCeyI sqYuzA4OzcMwnnTASvzsGZoYHTFP3DQwf2nzxD6yBGCfwNGIYfS0i8YN8XcBgEcDFMWpOQhT Pu3HeztMnF3HXrc0t7e5rDW9zCh3k2PA6D2NV4fews9KDFhLlTfCVzf0PS1dRVVWM+4jVl6l HRIAgWp+2/f8dx5vPc4Ycp4IsZN0l1h9uT7qm1KTwz+sSl1zOqKD/BpfGNZfLRRxrXthvvY8 BltcuZ4+PGFTcRkMytUbMDFMF9Cjd2W9dXD35PEtvj8wnEyzIos8bbgtLrGTv/SYhmPpahJA l8hPhYvmAvpOmusUUyB30StsHIU2LLccUPPOwU0ETofVZwEQALlLbQeBDTDbwQYrj0gbx3bq 7kpKABxN2MqeuqGr02DpS9883d/t7ontxasXoEz2GTioevvRmllJlPQERVxM8gQoNg22twF7 pB/zsrIjxkE9heE4wYfN1AyzT+AxgYN6f8hVQ7Nrc9XgZZe+8IkuW/Nf64KzNJXnSH4u6nJM J2+Dt274YoFcXR1nG76Q259mKwzbCukKbd6piL+VsT/qBrLhZe9Ivbjq5WMdkQKnP7gYKCAi pNVJC4enWfivZsYupMd9qn7Uv/oCZDYoBTdMSBUblaLMwlcjnPpOYK5rfHvC4opxl+P/Vzyz 6WC2TLkPtKvYvXmdsI6rnEI4Uucg0Au/Ulg7aqqKhzGPIbVaL+U0Wk82nz6hz+WP2ggTrY1w ZlPlRt8WM9w6WfLf2j+PuGklj37m+KvaOEfLsF1v464dSpy1tQVHhhp8LFTxh/6RWkRIR2uF I4v3Xu/k5D0LhaZHpQ4C+xKsQxpTGuYh2tnRaRL14YMW1dlI3HfeB2gj7Yc8XdHh9vkpPyuT nY/ZsFbnvBtiw7GchKKri2gDhRb2QNNDyBnQn5mRFw7CyuFclAksOdV/sdpQnYlYcRQWOUGY HhQ5eqTRZjm9z+qQe/T0HQpmiPTqQcIaG/edgKVTUjITfA7AJMKLQHgp04Vylb+G6jocnQQX JqvvP09whbqrABEBAAHCwWUEGAECAA8CGwwFAlVcpi8FCRmg08MACgkQyx8mb86fmYHNRQ/+ J0OZsBYP4leJvQF8lx9zif+v4ZY/6C9tTcUv/KNAE5leyrD4IKbnV4PnbrVhjq861it/zRQW cFpWQszZyWRwNPWUUz7ejmm9lAwPbr8xWT4qMSA43VKQ7ZCeTQJ4TC8kjqtcbw41SjkjrcTG wF52zFO4bOWyovVAPncvV9eGA/vtnd3xEZXQiSt91kBSqK28yjxAqK/c3G6i7IX2rg6pzgqh hiH3/1qM2M/LSuqAv0Rwrt/k+pZXE+B4Ud42hwmMr0TfhNxG+X7YKvjKC+SjPjqp0CaztQ0H nsDLSLElVROxCd9m8CAUuHplgmR3seYCOrT4jriMFBtKNPtj2EE4DNV4s7k0Zy+6iRQ8G8ng QjsSqYJx8iAR8JRB7Gm2rQOMv8lSRdjva++GT0VLXtHULdlzg8VjDnFZ3lfz5PWEOeIMk7Rj trjv82EZtrhLuLjHRCaG50OOm0hwPSk1J64R8O3HjSLdertmw7eyAYOo4RuWJguYMg5DRnBk WkRwrSuCn7UG+qVWZeKEsFKFOkynOs3pVbcbq1pxbhk3TRWCGRU5JolI4ohy/7JV1TVbjiDI HP/aVnm6NC8of26P40Pg8EdAhajZnHHjA7FrJXsy3cyIGqvg9os4rNkUWmrCfLLsZDHD8FnU mDW4+i+XlNFUPUYMrIKi9joBhu18ssf5i5Q= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 4/20/25 03:53, Carlos Maiolino wrote: > On Sun, Apr 20, 2025 at 02:47:02AM -0700, Guenter Roeck wrote: >> On Tue, Mar 25, 2025 at 09:10:49AM +0000, Hans Holmberg wrote: >>> Presently we start garbage collection late - when we start running >>> out of free zones to backfill max_open_zones. This is a reasonable >>> default as it minimizes write amplification. The longer we wait, >>> the more blocks are invalidated and reclaim cost less in terms >>> of blocks to relocate. >>> >>> Starting this late however introduces a risk of GC being outcompeted >>> by user writes. If GC can't keep up, user writes will be forced to >>> wait for free zones with high tail latencies as a result. >>> >>> This is not a problem under normal circumstances, but if fragmentation >>> is bad and user write pressure is high (multiple full-throttle >>> writers) we will "bottom out" of free zones. >>> >>> To mitigate this, introduce a zonegc_low_space tunable that lets the >>> user specify a percentage of how much of the unused space that GC >>> should keep available for writing. A high value will reclaim more of >>> the space occupied by unused blocks, creating a larger buffer against >>> write bursts. >>> >>> This comes at a cost as write amplification is increased. To >>> illustrate this using a sample workload, setting zonegc_low_space to >>> 60% avoids high (500ms) max latencies while increasing write >>> amplification by 15%. >>> >> ... >>> bool >>> xfs_zoned_need_gc( >>> struct xfs_mount *mp) >>> { >>> + s64 available, free; >>> + >> ... >>> + >>> + free = xfs_estimate_freecounter(mp, XC_FREE_RTEXTENTS); >>> + if (available < mult_frac(free, mp->m_zonegc_low_space, 100)) >>> + return true; >>> + >> >> With some 32-bit builds (parisc, openrisc so far): >> >> Error log: >> ERROR: modpost: "__divdi3" [fs/xfs/xfs.ko] undefined! >> ERROR: modpost: "__umoddi3" [fs/xfs/xfs.ko] undefined! >> ERROR: modpost: "__moddi3" [fs/xfs/xfs.ko] undefined! >> ERROR: modpost: "__udivdi3" [fs/xfs/xfs.ko] undefined! >> > > I opened a discussion about this: > > https://lore.kernel.org/lkml/20250419115157.567249-1-cem@kernel.org/ A possible local solution is below. Note the variable type change from s64 to u64. Guenter --- diff --git a/fs/xfs/xfs_zone_gc.c b/fs/xfs/xfs_zone_gc.c index 8c541ca71872..6dde2a680e75 100644 --- a/fs/xfs/xfs_zone_gc.c +++ b/fs/xfs/xfs_zone_gc.c @@ -170,7 +170,7 @@ bool xfs_zoned_need_gc( struct xfs_mount *mp) { - s64 available, free; + u64 available, free, rem; if (!xfs_group_marked(mp, XG_TYPE_RTG, XFS_RTG_RECLAIMABLE)) return false; @@ -183,7 +183,12 @@ xfs_zoned_need_gc( return true; free = xfs_estimate_freecounter(mp, XC_FREE_RTEXTENTS); - if (available < mult_frac(free, mp->m_zonegc_low_space, 100)) + + rem = do_div(free, 100); + free = free * mp->m_zonegc_low_space + + div_u64(rem * mp->m_zonegc_low_space, 100); + + if (available < free) return true; return false;