6d9df8a588
collapse_file() is using unmap_mapping_pages(1) on each small page found mapped, unlike others (reclaim, migration, splitting, memory-failure) who use try_to_unmap(). There are four advantages to try_to_unmap(): first, its TTU_IGNORE_MLOCK option now avoids leaving mlocked page in pagevec; second, its vma lookup uses i_mmap_lock_read() not i_mmap_lock_write(); third, it breaks out early if page is not mapped everywhere it might be; fourth, its TTU_BATCH_FLUSH option can be used, as in page reclaim, to save up all the TLB flushing until all of the pages have been unmapped. Wild guess: perhaps it was originally written to use try_to_unmap(), but hit the VM_BUG_ON_PAGE(page_mapped) after unmapping, because without TTU_SYNC it may skip page table locks; but unmap_mapping_pages() never skips them, so fixed the issue. I did once hit that VM_BUG_ON_PAGE() since making this change: we could pass TTU_SYNC here, but I think just delete the check - the race is very rare, this is an ordinary small page so we don't need to be so paranoid about mapcount surprises, and the page_ref_freeze() just below already handles the case adequately. Signed-off-by: Hugh Dickins <hughd@google.com> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> |
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|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.