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The existing comments in filemap_fault() suggest that, after either a minor fault has occurred and filemap_get_folio() found a folio in the page cache, or a major fault arose and __filemap_get_folio(FGP_CREATE...) did the job (having relied on do_sync_mmap_readahead() or filemap_read_folio() to read in the folio), the only possible reason it could not be uptodate is because of an error. This is not so, as if, for instance, the fault occurred within a VMA which had the VM_RAND_READ flag set (via madvise() with the MADV_RANDOM flag specified), this would cause even synchronous readahead to fail to read in the folio. I confirmed this by dropping page caches and faulting in memory madvise()'d this way, observing that this code path was reached on each occasion. Clarify the comments to include this case, and additionally update the comment recently added around the invalidate lock logic to make it clear the comment explicitly refers to the minor fault case. In addition, while we're here, refer to folios rather than pages. [lstoakes@gmail.com: correct identation as per Christopher's feedback] Link: https://lkml.kernel.org/r/2c7014c0-6343-4e76-8697-3f84f54350bd@lucifer.local Link: https://lkml.kernel.org/r/20230930231029.88196-1-lstoakes@gmail.com Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Christoph Hellwig <hch@lst.de> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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.