On giovedì 29 dicembre 2022 23:50:56 CEST 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(). Hi Al, I see that this series is here since Dec 29, 2022. Is there anything that prevents its merging? Can you please its four patches in your tree? Thanks, Fabio > > 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] > > Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > Cc: Ira Weiny <ira.weiny@xxxxxxxxx> > Signed-off-by: Fabio M. De Francesco <fmdefrancesco@xxxxxxxxx> > > 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. > > Changes from v3: > 1/3: No changes. > 2/3: No changes. > 3/3: Replace kunmap() with kunmap_local(). > > Changes from v4: > 1/4: It was 1/3. > 2/4: Move the declaration of a page into an inner loop. Add Ira > Weiny's "Reviewed-by" tag (thanks!). > 3/4: Add this patch to use ufs_put_page() to replace three kunmap() > and put_page() in namei.c. Thanks to Ira Weiny who noticed that > I had overlooked their presence. > 4/4: Remove an unnecessary masking that is already carried out by > kunmap_local() via kunmap_local_indexed(). Add a comment to > clarify that a ufs_dir_entry passed to ufs_delete_entry() > points in the same page we need the address of. Suggested by > Ira Weiny. > > [1] https://lore.kernel.org/lkml/Y4E++JERgUMoqfjG@ZenIV/#t > [2] https://lore.kernel.org/lkml/Y4FG0O7VWTTng5yh@ZenIV/#t > [3] https://lore.kernel.org/lkml/Y4ONIFJatIGsVNpf@ZenIV/#t > [4] https://lore.kernel.org/lkml/Y5Zc0qZ3+zsI74OZ@ZenIV/#t > [5] https://lore.kernel.org/lkml/Y5ZZy23FFAnQDR3C@ZenIV/#t > [6] https://lore.kernel.org/lkml/Y5ZcMPzPG9h6C9eh@ZenIV/#t > [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@xxxxxxxxx/ > The cover letter of the v2 series is at > https://lore.kernel.org/lkml/20221212231906.19424-1-fmdefrancesco@xxxxxxxxx/ > The cover letter of the v3 series is at > https://lore.kernel.org/lkml/20221217184749.968-1-fmdefrancesco@xxxxxxxxx/ > The cover letter of the v4 series is at > https://lore.kernel.org/lkml/20221221172802.18743-1-fmdefrancesco@xxxxxxxxx/ > > Fabio M. De Francesco (4): > fs/ufs: Use the offset_in_page() helper > fs/ufs: Change the signature of ufs_get_page() > fs/ufs: Use ufs_put_page() in ufs_rename() > fs/ufs: Replace kmap() with kmap_local_page() > > fs/ufs/dir.c | 131 +++++++++++++++++++++++++++---------------------- > fs/ufs/namei.c | 11 ++--- > fs/ufs/ufs.h | 1 + > 3 files changed, 78 insertions(+), 65 deletions(-) > > -- > 2.39.0
