Commit 0c867eca authored by Kirill Smelkov's avatar Kirill Smelkov

X io notes: Link to minor pagefault cost

parent f3e73456
...@@ -80,7 +80,9 @@ mmap ...@@ -80,7 +80,9 @@ mmap
The kernel handles both disk I/O and caching (in pagecache). The kernel handles both disk I/O and caching (in pagecache).
Cost ~ α (XXX recheck) is spent on first-time access. XXX the cost of minor pagefault is ~ 5.5·α http://marc.info/?l=linux-kernel&m=149002565506733&w=2
Cost ~ α (FIXME see ^^^) is spent on first-time access.
Future accesses to page, given it is still in page-cache, does not incur α cost. Future accesses to page, given it is still in page-cache, does not incur α cost.
However I/O errors are reported as SIGBUS on memory access. Thus if for read However I/O errors are reported as SIGBUS on memory access. Thus if for read
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// TODO copyright / license // Copyright (C) 2017 Nexedi SA and Contributors.
// Kirill Smelkov <kirr@nexedi.com>
//
// This program is free software: you can Use, Study, Modify and Redistribute
// it under the terms of the GNU General Public License version 2, or (at your
// option) any later version, as published by the Free Software Foundation.
//
// This program is distributed WITHOUT ANY WARRANTY; without even the implied
// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
//
// See COPYING file for full licensing terms.
// XXX move -> xbufio // XXX move -> xbufio
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