On 11:11 Втр 19 Июн , Alex Tomas wrote: > Mingming Cao wrote: > >>From the comments it says the page->private is set to 1 to letting > >commit_write know that it needs block reservation, but I don't see the > >page->private value being checked in ext4_wb_commit_write(). Instead, > >the PageMappedToDisk(page) flag is being checked. > > > >Alex, can you clarify the use of page->private and PagePrivate flag > >here? Do we still need the page->private for delayed allocation, with > >PageBooked flag and PageMappedToDisk page flag? > > sorry for confusion, we need PagePrivate so that truncate calls our > ->invalidatepage(). in turn this call is needed to drop unused reservation. > > block_read_full_page() must not happen to pages being delayed allocated > in the first place - it's uptodate by definition. I think the problem > began when ext4_wb_commit_write() exited due to -ENOSPC but left not > uptodate *and* with PG_private. then subsequent access to page turned to > block_read_full_page() which relies on PG_private and meaningful private > field. Dmitry, could you repeat the test with SetPagePrivate(page) moved > to after that if() with ext4_wb_reserve_space_page(), please? Yes it works. Bug not triggered now. But whole approach based on using PagePrivate bit and page->private ptr for special purposes is realy dengerous, and imho wrong, because avery fs-related code assume that page->private points to page_buffers. Especially this approach not work for blksize < pgsize. The best way to store/pass any block related info is buffer_head flags. This approach works for blksize < pgsize case too. > > > as i'm here ... status update: I've been reworking delayed allocation > patches to support blocksize < PAGE_CACHE_SIZE (and address akpm's request > for more generic implementation). the patch isn't ready for review, but > hopefully will be in few days. > > > thanks, Alex > > > - > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
