As the man page for proc describes, the "maps" file lists all the mapped
memory regions a process is using. Each line describes an area in that
process's memory space and what it's related to. The first field is an
address range (in hex), the second is the permissions on that address
space, the third is the offset into the file, then the device number,
then the inode, and finally the file itself.
With virtual memory mapping, a section of memory space can be made to
represent a device or file (or a selected part of one). This doesn't
mean that the file is really loaded into memory, but that if you *do*
refer to that memory space, the contents of that file are what you'll
get. The linked libraries, for instance, are mapped this way even if
they're not used. As a convenience, a programmer could memory-map a
whole CD, and then simply access it at random as if it was already
loaded into memory. The kernel will handle things like actually reading
or caching parts of the file. Other blocks of memory really are
allocated, such as for variables.
In the case of your listing, there are two particularly large blocks, on line
46:
00623000-60000000 ---p 00623000 00:00 0
which is a memory range of 1.5GB, and on line 260:
80000000-b7cf0000 ---p 80000000 00:00 0
which represents another 892MB. If you add up all the ranges for the maps
listing you give, you'll get 2593MB, which is pretty much what it says in your
top screenshot.
I don't know what those extra-big memory spaces are for, perhaps
somebody more familiar with Wine or the Linux process memory allocations
can say. Either way, the "VIRT" output of top shows the total amount of
such virtual memory spaces defined in the process. The "RES" column
indicates the actual amount of physical RAM currently in use by the
process.
** Changed in: procps (Ubuntu)
Status: New => Invalid
--
top shows one process using more memory than there is available
https://bugs.launchpad.net/bugs/76990
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