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sergey-senozhatskyakpm00
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zsmalloc: document new fullness grouping
Patch series "zsmalloc: minor documentation updates". Two minor patches that bring zsmalloc documentation up to date. This patch (of 2): Update documentation and reflect new zspages fullness grouping (we don't use almost_empty and almost_full anymore). Link: https://lkml.kernel.org/r/20230325024631.2817153-1-senozhatsky@chromium.org Link: https://lkml.kernel.org/r/20230325024631.2817153-2-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org> Fixes: 67e157e ("zsmalloc: show per fullness group class stats") Cc: Minchan Kim <minchan@kernel.org> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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‎Documentation/mm/zsmalloc.rst‎

Lines changed: 74 additions & 59 deletions
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@@ -39,13 +39,12 @@ With CONFIG_ZSMALLOC_STAT, we could see zsmalloc internal information via
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# cat /sys/kernel/debug/zsmalloc/zram0/classes
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class size almost_full almost_empty obj_allocated obj_used pages_used pages_per_zspage
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class size 10% 20% 30% 40% 50% 60% 70% 80% 90% 99% 100% obj_allocated obj_used pages_used pages_per_zspage freeable
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...
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...
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9 176 0 1 186 129 8 4
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10 192 1 0 2880 2872 135 3
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11 208 0 1 819 795 42 2
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12 224 0 1 219 159 12 4
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30 512 0 12 4 1 0 1 0 0 1 0 414 3464 3346 433 1 14
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31 528 2 7 2 2 1 0 1 0 0 2 117 4154 3793 536 4 44
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32 544 6 3 4 1 2 1 0 0 0 1 260 4170 3965 556 2 26
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...
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...
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@@ -54,10 +53,28 @@ class
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index
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size
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object size zspage stores
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almost_empty
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the number of ZS_ALMOST_EMPTY zspages(see below)
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almost_full
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the number of ZS_ALMOST_FULL zspages(see below)
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10%
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the number of zspages with usage ratio less than 10% (see below)
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20%
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the number of zspages with usage ratio between 10% and 20%
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30%
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the number of zspages with usage ratio between 20% and 30%
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40%
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the number of zspages with usage ratio between 30% and 40%
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50%
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the number of zspages with usage ratio between 40% and 50%
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60%
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the number of zspages with usage ratio between 50% and 60%
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70%
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the number of zspages with usage ratio between 60% and 70%
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80%
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the number of zspages with usage ratio between 70% and 80%
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90%
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the number of zspages with usage ratio between 80% and 90%
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99%
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the number of zspages with usage ratio between 90% and 99%
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100%
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the number of zspages with usage ratio 100%
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obj_allocated
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the number of objects allocated
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obj_used
@@ -67,18 +84,11 @@ pages_used
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pages_per_zspage
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the number of 0-order pages to make a zspage
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We assign a zspage to ZS_ALMOST_EMPTY fullness group when n <= N / f, where
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* n = number of allocated objects
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* N = total number of objects zspage can store
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* f = fullness_threshold_frac(ie, 4 at the moment)
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Similarly, we assign zspage to:
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* ZS_ALMOST_FULL when n > N / f
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* ZS_EMPTY when n == 0
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* ZS_FULL when n == N
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Each zspage maintains inuse counter which keeps track of the number of
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objects stored in the zspage. The inuse counter determines the zspage's
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"fullness group" which is calculated as the ratio of the "inuse" objects to
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the total number of objects the zspage can hold (objs_per_zspage). The
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closer the inuse counter is to objs_per_zspage, the better.
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Internals
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=========
@@ -94,10 +104,10 @@ of objects that each zspage can store.
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For instance, consider the following size classes:::
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class size almost_full almost_empty obj_allocated obj_used pages_used pages_per_zspage freeable
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class size 10% .... 100% obj_allocated obj_used pages_used pages_per_zspage freeable
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...
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94 1536 0 0 0 0 0 3 0
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100 1632 0 0 0 0 0 2 0
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94 1536 0 .... 0 0 0 0 3 0
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100 1632 0 .... 0 0 0 0 2 0
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...
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@@ -134,10 +144,11 @@ reduces memory wastage.
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Let's take a closer look at the bottom of `/sys/kernel/debug/zsmalloc/zramX/classes`:::
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class size almost_full almost_empty obj_allocated obj_used pages_used pages_per_zspage freeable
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class size 10% .... 100% obj_allocated obj_used pages_used pages_per_zspage freeable
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...
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202 3264 0 0 0 0 0 4 0
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254 4096 0 0 0 0 0 1 0
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202 3264 0 .. 0 0 0 0 4 0
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254 4096 0 .. 0 0 0 0 1 0
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...
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Size class #202 stores objects of size 3264 bytes and has a maximum of 4 pages
@@ -151,40 +162,42 @@ efficient storage of large objects.
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For zspage chain size of 8, huge class watermark becomes 3632 bytes:::
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class size almost_full almost_empty obj_allocated obj_used pages_used pages_per_zspage freeable
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class size 10% .... 100% obj_allocated obj_used pages_used pages_per_zspage freeable
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...
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202 3264 0 0 0 0 0 4 0
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211 3408 0 0 0 0 0 5 0
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217 3504 0 0 0 0 0 6 0
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222 3584 0 0 0 0 0 7 0
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225 3632 0 0 0 0 0 8 0
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254 4096 0 0 0 0 0 1 0
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202 3264 0 .. 0 0 0 0 4 0
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211 3408 0 .. 0 0 0 0 5 0
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217 3504 0 .. 0 0 0 0 6 0
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222 3584 0 .. 0 0 0 0 7 0
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225 3632 0 .. 0 0 0 0 8 0
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254 4096 0 .. 0 0 0 0 1 0
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...
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For zspage chain size of 16, huge class watermark becomes 3840 bytes:::
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class size almost_full almost_empty obj_allocated obj_used pages_used pages_per_zspage freeable
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class size 10% .... 100% obj_allocated obj_used pages_used pages_per_zspage freeable
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...
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202 3264 0 0 0 0 0 4 0
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206 3328 0 0 0 0 0 13 0
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207 3344 0 0 0 0 0 9 0
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208 3360 0 0 0 0 0 14 0
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211 3408 0 0 0 0 0 5 0
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212 3424 0 0 0 0 0 16 0
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214 3456 0 0 0 0 0 11 0
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217 3504 0 0 0 0 0 6 0
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219 3536 0 0 0 0 0 13 0
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222 3584 0 0 0 0 0 7 0
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223 3600 0 0 0 0 0 15 0
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225 3632 0 0 0 0 0 8 0
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228 3680 0 0 0 0 0 9 0
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230 3712 0 0 0 0 0 10 0
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232 3744 0 0 0 0 0 11 0
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234 3776 0 0 0 0 0 12 0
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235 3792 0 0 0 0 0 13 0
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236 3808 0 0 0 0 0 14 0
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238 3840 0 0 0 0 0 15 0
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254 4096 0 0 0 0 0 1 0
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202 3264 0 .. 0 0 0 0 4 0
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206 3328 0 .. 0 0 0 0 13 0
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207 3344 0 .. 0 0 0 0 9 0
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208 3360 0 .. 0 0 0 0 14 0
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211 3408 0 .. 0 0 0 0 5 0
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212 3424 0 .. 0 0 0 0 16 0
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214 3456 0 .. 0 0 0 0 11 0
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217 3504 0 .. 0 0 0 0 6 0
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219 3536 0 .. 0 0 0 0 13 0
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222 3584 0 .. 0 0 0 0 7 0
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223 3600 0 .. 0 0 0 0 15 0
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225 3632 0 .. 0 0 0 0 8 0
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228 3680 0 .. 0 0 0 0 9 0
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230 3712 0 .. 0 0 0 0 10 0
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232 3744 0 .. 0 0 0 0 11 0
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234 3776 0 .. 0 0 0 0 12 0
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235 3792 0 .. 0 0 0 0 13 0
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236 3808 0 .. 0 0 0 0 14 0
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238 3840 0 .. 0 0 0 0 15 0
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254 4096 0 .. 0 0 0 0 1 0
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...
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Overall the combined zspage chain size effect on zsmalloc pool configuration:::
@@ -214,9 +227,10 @@ zram as a build artifacts storage (Linux kernel compilation).
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zsmalloc classes stats:::
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class size almost_full almost_empty obj_allocated obj_used pages_used pages_per_zspage freeable
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class size 10% .... 100% obj_allocated obj_used pages_used pages_per_zspage freeable
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...
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Total 13 51 413836 412973 159955 3
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Total 13 .. 51 413836 412973 159955 3
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zram mm_stat:::
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@@ -227,9 +241,10 @@ zram as a build artifacts storage (Linux kernel compilation).
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zsmalloc classes stats:::
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class size almost_full almost_empty obj_allocated obj_used pages_used pages_per_zspage freeable
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class size 10% .... 100% obj_allocated obj_used pages_used pages_per_zspage freeable
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...
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Total 18 87 414852 412978 156666 0
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Total 18 .. 87 414852 412978 156666 0
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zram mm_stat:::
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