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comparison OrthancServer/Resources/ImplementationNotes/memory_consumption.txt @ 5159:f5907aecbaed

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conditional usage of malloc_trim
author Alain Mazy <am@osimis.io>
date Thu, 02 Feb 2023 11:28:35 +0100
parents 02cfd23a556a
children 566e8d32bd3a
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5158:02cfd23a556a 5159:f5907aecbaed
109 from the system. 109 from the system.
110 110
111 Malloc_trim returns 1 if it actually released any memory, else 0. 111 Malloc_trim returns 1 if it actually released any memory, else 0.
112 On systems that do not support "negative sbrks", it will always 112 On systems that do not support "negative sbrks", it will always
113 return 0. 113 return 0.
114
115
116 glibc internals
117 ---------------
118
119 Lots of useful info here: https://man7.org/linux/man-pages/man3/mallopt.3.html
120
121 summary:
122 - malloc uses sbrk() or mmap() to allocate memory. mmap() is used to allocate
123 large memory chunks, larger than M_MMAP_THRESHOLD.
124 - about mmap(): On the other hand, there are some disadvantages to
125 the use of mmap(2): deallocated space is not placed on the
126 free list for reuse by later allocations; memory may be
127 wasted because mmap(2) allocations must be page-aligned;
128 and the kernel must perform the expensive task of zeroing
129 out memory allocated via mmap(2). Balancing these factors
130 leads to a default setting of 128*1024 for the
131 M_MMAP_THRESHOLD parameter.
132 - free() employs sbrk() to release memory back to the system and M_TRIM_THRESHOLD
133 specifies the minimum size that is released. So, even without
134 malloc_trim, Orthanc is able to give back memory to the system.
135 - free() never gives back block allocated by mmap() to the system, only malloc_trim() does !