mmap is a POSIX-compliant Unix system call that maps files or devices into memory.
mmap() creates a new mapping in the virtual address space of the calling process.
Questions tagged [mmap]
1936 questions
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votes
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Unmapping or 'release' a MappedByteBuffer under Android
The usual problem in Java is that you have to hack to get a proper unmapping of memory mapped files - see here for the 14year old bug report ;)
But on Android there seems to be 0 solutions in pure Java and just via NDK. Is this true? If yes, any…
Karussell
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6 answers
Why doesn't POSIX mmap return a volatile void*?
Mmap returns a void*, but not a volatile void*. If I'm using mmap to map shared memory, then another process could be writing to that memory, which means two subsequent reads from the same memory location can yield different values -- the exact…
Joseph Garvin
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Why use mmap over fread?
Why/when is it better to use mmap(), as opposed to fread()'ing from a filestream in chunks into a byte array?
uint8_t my_buffer[MY_BUFFER_SIZE];
size_t bytes_read;
bytes_read = fread(my_buffer, 1, sizeof(my_buffer), input_file);
if (MY_BUFFER_SIZE…
tarabyte
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Android NDK mmap call broken on 32-bit devices after upgrading to Lollipop
I'm trying to grab 784 MiB of memory. Yes, I know that is a lot for a 32-bit phone, but the following call worked before Android 5.0:
mmap(0, 0x31000000, PROT_NONE, MAP_ANON | MAP_SHARED, -1, 0);
However, on three different devices from different…
sigmabeta
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Why mmap cannot allocate memory?
I ran the program with root priviledge but it keeps complaining that mmap cannot allocate memory. Code snippet is below:
#define PROTECTION (PROT_READ | PROT_WRITE)
#define LENGTH (4*1024)
#ifndef MAP_HUGETLB
#define MAP_HUGETLB…
drdot
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3 answers
JVM cant map reserved memory when running in Docker container
I cant seem to run java at all in a Docker container on my server. Even when issuing java -version, I get the following error.
root@86088d679103:/# java -version
OpenJDK 64-Bit Server VM warning: INFO: os::commit_memory(0x0000035ce1000000, 2555904,…
KayoticSully
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Bad Linux Memory Mapped File Performance with Random Access C++ & Python
While trying to use memory mapped files to create a multi-gigabyte file (around 13gb), I ran into what appears to be a problem with mmap(). The initial implementation was done in c++ on Windows using boost::iostreams::mapped_file_sink and all was…
shao.lo
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Segfault reading lazy bytestring past 2^18 bytes
Consider the following code: http://hpaste.org/90394
I am memory mapping a large 460mb file to a lazy ByteString. The length of the ByteString reports 471053056.
When nxNodeFromID file 110000 is changed to a lower node ID, ie: 10000, it works…
kvanbere
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4 answers
Java OutOfMemory exception: mmap error on loading zip file
I run my app on production env (rhel 5.2 x64, oracle jre 1.7_05, tomcat 7.0.28) with JVM arguments:
-Xms8192m -Xmx8192m -XX:MaxPermSize=1024m
-Doracle.net.tns_admin=/var/ora_net -XX:ReservedCodeCacheSize=512m -XX:+AggressiveOpts…
Darya Dmitrichenko
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How to use /dev/kmem?
Updated my post...
I got below program. It operates on /dev/kmem and /dev/mem.
I think I can learn something from the code. But when I run it on my Beagle Board, below result is given:
case 1: ( if(1) )
root@omap:/home/ubuntu/tom# ./kmem_mem…
Tom Xue
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Solr uses too much memory
We have a Solr 3.4 instance running on Windows 2008 R2 with Oracle Java 6 Hotspot JDK that becomes unresponsive. When we looked at the machine, we noticed that the available physical memory went to zero.
The Tomcat7.exe process was using ~70Gigs…
rjdevereux
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Implementing your own malloc/free with mmap and munmap
I have implemented by own malloc and free using mmap. Now since unlike free, munmap also takes length as parameter, therefore I put length as an additional information in the mapped memory.
The code for my malloc and free is shown below. I want to…
MetallicPriest
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mmap and csv files
I am trying to understand how to use the package mmap
to access large csv files. More precisely, I'd like to
Create a mmap object from a csv file with mmap.csv();
Save the file created by mmap.csv() containing the data in binary format;
Be able to…
Ryogi
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Is mmap atomic?
Are mmap calls atomic in their effect?
That is, does a mapping change made by mmap appear atomically to other threads accessing the affected region?
As a litmus test, consider the case you do a mmap in a file of all zeros (from thread T1 which is…
BeeOnRope
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communicating between processes with shared-memory results zero-copy?
I am writing a network daemon, on Linux with kernel 2.6, which has
one producer process and N of consumer processes, which does not make any change on the data, and does not create any response back to the producer.
Whenever the producer process…
ddoman
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