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authorRich Felker <dalias@libc.org>2015-12-09 19:37:53 +0000
committerRich Felker <dalias@libc.org>2016-04-28 20:47:50 +0000
commit511bc46f2afc11ccb966c65391fe6488e82d05b9 (patch)
tree49b53c729226f470c292651720d74dd47c33951b /net
parent09facf50a3243f5ea54c863a22f2b1f4ca6b0376 (diff)
downloadlinux-sh-511bc46f2afc11ccb966c65391fe6488e82d05b9.tar.gz
ramfs: fix VM_MAYSHARE mappings for NOMMU
The nommu do_mmap expects f_op->get_unmapped_area to either succeed or return -ENOSYS for VM_MAYSHARE (e.g. private read-only) mappings. Returning addr in the non-MAP_SHARED case was completely wrong, and only happened to work because addr was 0. However, it prevented VM_MAYSHARE mappings from sharing backing with the fs cache, and forced such mappings (including shareable program text) to be copied whenever the number of mappings transitioned from 0 to 1, impacting performance and memory usage. Subsequent mappings beyond the first still correctly shared memory with the first. Instead, treat VM_MAYSHARE identically to VM_SHARED at the file ops level; do_mmap already handles the semantic differences between them. Signed-off-by: Rich Felker <dalias@libc.org>
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