mirror of https://github.com/mkerrisk/man-pages
f90b94e32c
Looking at the code in mm/fadvise.c, we have
case POSIX_FADV_DONTNEED:
if (!inode_write_congested(mapping->host))
__filemap_fdatawrite_range(mapping, offset, endbyte,
WB_SYNC_NONE);
This suggests that *if* the backing device is not congested, then
__filemap_fdatawrite_range() is called. The comments for that
function say:
__filemap_fdatawrite_range - start writeback on mapping dirty pages in range
So, my reading of this is that *maybe* some dirty pages will be
written to the backing device by the time that POSIX_FADV_DONTNEED
gets to calling invalidate_mapping_pages() whose description says:
/**
* invalidate_mapping_pages - Invalidate all the unlocked pages of one inode
* @mapping: the address_space which holds the pages to invalidate
* @start: the offset 'from' which to invalidate
* @end: the offset 'to' which to invalidate (inclusive)
*
* This function only removes the unlocked pages, if you want to
* remove all the pages of one inode, you must call truncate_inode_pages.
*
* invalidate_mapping_pages() will not block on IO activity. It will not
* invalidate pages which are dirty, locked, under writeback or mapped into
* pagetables.
*/
So, my reading of this is that the handling of dirty pages is an
optimization. If some pages can be written in time, they will be
freed by POSIX_MADV_DONTFREE. But there are no guarantees.
All of that said, some experimentation suggests that, in a lot
of cases, POSIX_MADV_DONTFREE does often free dirty pages.
See https://bugzilla.kernel.org/show_bug.cgi?id=95421.
Reported-by: Maik Zumstrull <maik@zumstrull.net>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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| man-pages-4.10.lsm | ||
README
This package contains Linux man pages for sections 2, 3, 4, 5, and 7. Some more information is given in the `Announce' file. Install by copying to your favourite location. "make install" will just copy them to /usr/share/man/man[1-8]. To install to a path different from /usr use "make install prefix=/install/path". "make" will move the pages from this package that are older than the already installed ones to a subdirectory `not_installed', then remove old versions (compressed or not), compress the pages, and copy them to /usr/share/man/man[1-8]. Note that you may have to remove preformatted pages. Note that sometimes these pages are duplicates of pages also distributed in other packages. This has been reported about dlclose.3, dlerror.3, dlopen.3, dlsym.3 (found in ld.so), about resolver.3, resolv.conf.5 (found in bind-utils), and about passwd.5, and mailaddr.7. Be careful not to overwrite more up-to-date versions. Reports on further duplicates are welcome. Formerly present and now removed duplicates: exports.5 (found in nfs-server-2.2*), fstab.5, nfs.5 (found in util-linux-2.12*), lilo.8, lilo.conf.5 (found in lilo-21.6*). Copyrights: These man pages come under various copyrights. All pages are freely distributable when the nroff source is included. If you have corrections and additions to suggest, see http://www.kernel.org/doc/man-pages/contributing.html