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0c4f8ed498
Currently in shrink_folio_list(), reclaim for folios under writeback falls into 3 different cases: 1) Reclaim is encountering an excessive number of folios under writeback and this folio has both the writeback and reclaim flags set 2) Dirty throttling is enabled (this happens if reclaim through cgroup is not enabled, if reclaim through cgroupv2 memcg is enabled, or if reclaim is on the root cgroup), or if the folio is not marked for immediate reclaim, or if the caller does not have __GFP_FS (or __GFP_IO if it's going to swap) set 3) Legacy cgroupv1 encounters a folio that already has the reclaim flag set and the caller did not have __GFP_FS (or __GFP_IO if swap) set In cases 1) and 2), we activate the folio and skip reclaiming it while in case 3), we wait for writeback to finish on the folio and then try to reclaim the folio again. In case 3, we wait on writeback because cgroupv1 does not have dirty folio throttling, as such this is a mitigation against the case where there are too many folios in writeback with nothing else to reclaim. If a filesystem (eg fuse) may deadlock due to reclaim waiting on writeback, then the filesystem needs to add inefficient messy workarounds to prevent this. To improve the performance of these filesystems, this commit adds two things: a) a AS_WRITEBACK_MAY_DEADLOCK_ON_RECLAIM mapping flag that filesystems may set to indicate that reclaim should not wait on writeback b) if legacy memcg encounters a folio with this AS_WRITEBACK_MAY_DEADLOCK_ON_RECLAIM flag set (eg case 3), the folio will be activated and skip reclaim (eg default to behavior in case 2) instead. Signed-off-by: Joanne Koong <joannelkoong@gmail.com> Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev> Reviewed-by: Jeff Layton <jlayton@kernel.org> Acked-by: David Hildenbrand <david@redhat.com> Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
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Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
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https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText 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.