| Message ID | 20221217184749.968-1-fmdefrancesco@gmail.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | fs/ufs: replace kmap() with kmap_local_page | expand |
On sabato 17 dicembre 2022 19:47:46 CET Fabio M. De Francesco wrote: > kmap() is being deprecated in favor of kmap_local_page(). > > There are two main problems with kmap(): (1) It comes with an overhead as > the mapping space is restricted and protected by a global lock for > synchronization and (2) it also requires global TLB invalidation when the > kmap’s pool wraps and it might block when the mapping space is fully > utilized until a slot becomes available. > > With kmap_local_page() the mappings are per thread, CPU local, can take > page faults, and can be called from any context (including interrupts). > It is faster than kmap() in kernels with HIGHMEM enabled. Furthermore, > the tasks can be preempted and, when they are scheduled to run again, the > kernel virtual addresses are restored and still valid. > > Since its use in fs/ufs is safe everywhere, it should be preferred. > > Therefore, replace kmap() with kmap_local_page() in fs/ufs. kunmap_local() > requires the mapping address, so return that address from ufs_get_page() > to be used in ufs_put_page(). > > This series could have not been ever made because nothing prevented the > previous patch from working properly but Al Viro made a long series of > very appreciated comments about how many unnecessary and redundant lines > of code I could have removed. He could see things I was entirely unable > to notice. Furthermore, he also provided solutions and details about how > I could decompose a single patch into a small series of three > independent units.[1][2][3] > > I want to thank him so much for the patience, kindness and the time he > decided to spend to provide those analysis and write three messages full > of interesting insights.[1][2][3] > > Changes from v1: > 1/3: No changes. > 2/3: Restore the return of "err" that was mistakenly deleted > together with the removal of the "out" label in > ufs_add_link(). Thanks to Al Viro.[4] > Return the address of the kmap()'ed page instead of a > pointer to a pointer to the mapped page; a page_address() > had been overlooked in ufs_get_page(). Thanks to Al > Viro.[5] > 3/3: Return the kernel virtual address got from the call to > kmap_local_page() after conversion from kmap(). Again > thanks to Al Viro.[6] > > Changes from v2: > 1/3: No changes. > 2/3: Rework ufs_get_page() because the previous version had two > errors: (1) It could return an invalid pages with the out > argument "page" and (2) it could return "page_address(page)" > also in cases where read_mapping_page() returned an error > and the page is never kmap()'ed. Thanks to Al Viro.[7] > 3/3: Rework ufs_get_page() after conversion to > kmap_local_page(), in accordance to the last changes in 2/3. > > [1] https://lore.kernel.org/lkml/Y4E++JERgUMoqfjG@ZenIV/ > [2] https://lore.kernel.org/lkml/Y4FG0O7VWTTng5yh@ZenIV/ > [3] https://lore.kernel.org/lkml/Y4ONIFJatIGsVNpf@ZenIV/ > [4] https://lore.kernel.org/lkml/Y5Zc0qZ3+zsI74OZ@ZenIV/ > [5] https://lore.kernel.org/lkml/Y5ZZy23FFAnQDR3C@ZenIV/ > [6] https://lore.kernel.org/lkml/Y5ZcMPzPG9h6C9eh@ZenIV/ > [7] https://lore.kernel.org/lkml/Y5glgpD7fFifC4Fi@ZenIV/#t > > The cover letter of the v1 series is at > https://lore.kernel.org/lkml/20221211213111.30085-1-fmdefrancesco@gmail.com/ > The cover letter of the v2 series is at > https://lore.kernel.org/lkml/20221212231906.19424-1-fmdefrancesco@gmail.com/ > > Fabio M. De Francesco (3): > fs/ufs: Use the offset_in_page() helper > fs/ufs: Change the signature of ufs_get_page() > fs/ufs: Replace kmap() with kmap_local_page() > > fs/ufs/dir.c | 134 +++++++++++++++++++++++++++------------------------ > 1 file changed, 71 insertions(+), 63 deletions(-) > > -- > 2.39.0 Please drop this v3 because of a mistake in patch 3/3. The updated v4 series is at https://lore.kernel.org/lkml/20221221172802.18743-1-fmdefrancesco@gmail.com/T/ Thanks, Fabio