在CentOS 7.3.1611（linux内核3.10）上，我的程序是使用缓冲区I / O 读取磁盘设备的I / O绑定，一般linux内核可能会使用完整内存来缓存磁盘数据作为缓冲区，但它总是留下大约20G未使用的内存，并且kswapd守护程序始终保持回收页面。
顶
top - 14:11:47 up 16 days, 2:42, 5 users, load average: 2.92, 3.18, 3.37
Tasks: 329 total, 2 running, 327 sleeping, 0 stopped, 0 zombie
%Cpu(s): 3.3 us, 7.7 sy, 0.0 ni, 83.3 id, 4.7 wa, 0.0 hi, 1.1 si, 0.0 st
KiB Mem : 13175558+total, 22444704 free, 26496388 used, 82814488 buff/cache
KiB Swap: 0 total, 0 free, 0 used. 10222934+avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
181 root 20 0 0 0 0 S 13.0 0.0 1395:34 kswapd0
cat / proc / meminfo
MemTotal: 131755580 kB
MemFree: 21335956 kB
MemAvailable: 102232248 kB
Buffers: 75100216 kB
Cached: 6990768 kB
SwapCached: 0 kB
Active: 69447392 kB
Inactive: 38154608 kB
Active(anon): 26890392 kB
Inactive(anon): 709920 kB
Active(file): 42557000 kB
Inactive(file): 37444688 kB
Unevictable: 0 kB
Mlocked: 0 kB
SwapTotal: 0 kB
SwapFree: 0 kB
Dirty: 180 kB
Writeback: 0 kB
AnonPages: 25511156 kB
Mapped: 35036 kB
Shmem: 2090184 kB
Slab: 1835540 kB
SReclaimable: 1684472 kB
SUnreclaim: 151068 kB
KernelStack: 15536 kB
PageTables: 59556 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
WritebackTmp: 0 kB
CommitLimit: 65877788 kB
Committed_AS: 5750772 kB
VmallocTotal: 34359738367 kB
VmallocUsed: 551220 kB
VmallocChunk: 34358888444 kB
HardwareCorrupted: 0 kB
AnonHugePages: 21006336 kB
HugePages_Total: 0
HugePages_Free: 0
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 2048 kB
DirectMap4k: 294840 kB
DirectMap2M: 11159552 kB
DirectMap1G: 124780544 kB
cat / proc / buddyinfo
Node 0, zone DMA 1 0 1 0 2 1 1 0 1 1 3
Node 0, zone DMA32 785 898 869 489 260 227 442 316 142 0 0
Node 0, zone Normal 71568 1575732 446338 39 9 0 0 0 0 0 0
sar -B -r 1
Linux 3.10.0-514.el7.x86_64 (PZ-R-01) 02/09/2018 _x86_64_ (32 CPU)
02:13:57 PM pgpgin/s pgpgout/s fault/s majflt/s pgfree/s pgscank/s pgscand/s pgsteal/s %vmeff
02:13:58 PM 139388.00 48.00 4622.00 0.00 399474.00 0.00 17844.00 17908.00 100.36
02:13:57 PM kbmemfree kbmemused %memused kbbuffers kbcached kbcommit %commit kbactive kbinact kbdirty
02:13:58 PM 20986792 110768788 84.07 75421044 7021576 5743480 4.36 69832168 38119340 200
似乎免费的内存页面已经足够了，为什么kswapd仍在回收页面？
// 2018/3/13更新
当更新linux内核从3.10到4.4时，它可以使用几乎完整的内存来缓存磁盘数据，因此它必须由kswapd行为引起，并且linux内核3.11改进了页面回收行为。